possible to mix bmax and sdk?

Is it possible to use any bmax drawing functions with the sdk?
or do you need to only use the sdk drawing comands.

Just the SDK drawing commands.

Are all the other non gfx bmax commands available?

Mostly, yes. Sound, input, gfx is all there. No networking or file stuff. See here for command list:
http://blitzmax.com/Products/blitz3dsdk.php

I meant the native bmax commands, can i continue to use those or am i locked into what the sdk supports?

You have all bmax commands and maxgui commands as usual.