I guess it depends how deep... And how much stress it's under... Cant really help soz, but I have ridden some severely scratched seatposts without a second thought
the seatpost is scratched (and it's alloy) is it safe?
Scratches in line with the axis are basically OK. Circumferential scratches above the clamp are potentially problematic, as the main stress crosses the scratch.
Yeah sanding isn't A problem, more now the seatpost is scratched (and it's alloy) is it safe?
#marathonman