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On the other hand, is it likely that Western governments are arming Syrian rebels / terrorists / anti-government guerillas / insurgents (delete label according to taste)?

The attempts by the US and others to obtain UN approval for armed action in Syria indicates a desire to use force against the Assad government, so yes, on balance, it seems likely.

"In Homs on Tuesday, a general claiming to be from the rebel group appeared on camera and told a journalist from Reuters news agency that “French and American assistance has reached us and is with us.” When asked to elaborate on the nature of the assistance he added, “We now have weapons and anti-aircraft missiles and, God willing, with all of that we will defeat Bashar [President Assad].”
-- http://blog.alexanderhiggins.com/2012/02/29/syria-terrorists-admit-france-supplying-weapons-88182/

"Syrian media have reported the arrests of French officers during security operations. RT’s Maria Finoshina says France has responded to the claims by returning its Ambassador to Damascus. This follows claims by the Free Syrian Army that it had received anti-aircraft missiles and other weapons from French and American sources."
-- https://rt.com/news/syrian-rebels-retreat-homs-607/

"The government of Syria says According to them, a brigade of 120 French soldiers part of a transmission unit came to support the rebels were caught by forces loyal to the Syrian regime in the region of Zabadani, after they took control of a key neighborhood in the city of homes Homs."
-- http://blog.alexanderhiggins.com/2012/03/01/report-120-french-troops-supporting-syria-rebels-captured-89202/

'On Monday, Qatar's prime minister declared his state's intent to start helping the Syrian opposition "by all means", including giving them weapons. Two days later, anti-Assad officials received an offer of a $100m (£63m) donation, from their brothers in arms in Libya. Coincidence? Unlikely, if the Libyan revolution is any indicator.
...
Qatar's remarks this week, as well as Saudi Arabia's claim last Friday that arming the Syrian rebels would be an "excellent idea", clearly shows a new reality. The Rubicon has been crossed. Hopes of resolving Syria's raging insurgency through patience, or dialogue, have evaporated."
-- http://www.guardian.co.uk/world/2012/mar/01/syria-conflict-rebels-qatar-weapons

When did the West promote a peaceful resolution?
"On February 4, Western politicians and journalists responded with outrage to the Russian and Chinese vetoing of a UN security council resolution calling for Syrian president Bashar Assad to step down as part of a ‘political transition’.
...
The corporate media took the same view. A leading article in the Independent commented:
‘Hillary Clinton described the vetoing of the UN resolution as a “travesty”. She is right. But this cannot be the international community's last word.’

Curiously, while Hague talked of the West’s determination ‘to find an end to the violence’, and the media railed against the Russians and Chinese for failing to seek the same, almost no-one noticed that the resolution had itself subordinated the possibility of a ceasefire to the demand for regime change.

The draft resolution did call ‘for an immediate end to all violence’. But it specifically demanded ‘that the Syrian government… withdraw all Syrian military and armed forces from cities and towns, and return them to their original home barracks’.

This one-sided demand that only Syrian government forces should withdraw from the streets closely resembled the Machiavellian device built into UN Resolution 1973 on Libya, passed on March 17, 2011.

This also called for ‘the immediate establishment of a cease-fire’ supported by ‘a ban on all flights’ in Libyan airspace. But crucially, the determination was added ‘to take all necessary measures… to protect civilians and civilian populated areas under threat of attack in the Libyan Arab Jamahiriya, including Benghazi…’

This clearly had nothing to do with the mere banning of flights. Indeed, the authorisation to protect civilians by ‘all necessary means’ transformed Nato planes from neutral monitors of Libyan airspace into a ground-attack air force for ‘rebel’ fighters.

Far from bringing an end to the violence, UN Resolution 1973 unleashed overwhelming Western force in pursuit of regime change, in a war that was fought to the bitter end. To ensure the right outcome, Western and other powers supplied special forces and weapons, simply ignoring the resolution's call for 'strict implementation of the arms embargo' and 'excluding a foreign occupation force of any form on any part of Libyan territory'. In short, the resolution resulted in a massive escalation in violence. Seumas Milne noted in the Guardian last week:
‘When it began, the death toll was 1,000 to 2,000. By the time Muammar Gaddafi was captured and lynched seven months later, it was estimated at more than 10 times that figure. The legacy of foreign intervention in Libya has also been mass ethnic cleansing, torture and detention without trial, continuing armed conflict, and a western-orchestrated administration so unaccountable it resisted revealing its members' names.’"
-- http://www.medialens.org/index.php?option=com_content&view=article&id=665:travesty-un-resolutions-of-mass-destruction-part-1&catid=25:alerts-2012&Itemid=9