i'm still pretty new to maya but here's my opinion.
I don't think you can extrude a vertex. but you can however move a vertex and it'll mimic as though it is being extruded. Unless if you're taking about extruding a vertex so it creates a single line away from the surface, then you would porbably want to deal with curves instead.
not sure if this is any help, just thought i give it a try
9 months into Maya...and still learning...
0 experience with any other 3D programs