Of course it is. It's actually a lot easier, as there are no envelopes and just one sample per instrument. Firehawk/TDA wrote this excellent player a while back: http://mod.haxor.fi/Purple_Motion/2nd_pm.s3m
I always wished I knew how to work ST3. I ended up instead mailing away for a copy of Modedit shortly before the really user-friendly FT2 was released.