The steam oven we are just about to put into production is designed for mid wall and under bench install.
The only thing i would say is the air which comes out of the exhaust duct can be quite high humidity so you might get a damp crotch if you are also chopping veg above your oven.
I'm going to be in the market for a new oven - steam looks interesting. Is it a no-no to put a steam oven under-counter?
Also....jeebus... plumbed in steam combis are even more expensive than I'd imagined!