It may be possible, but not likely. JK2 had a several limits on elements (models, brushes, etc) that were hard coded into the engine. Loading SP maps in MP would crash due to too many of these. Plus it would take a lot of tweaking to get them playable with two people online anyway.
Jedi Academy is a bit more realistic in this way because the limits have been significantly upped in the engine by Raven. OJP is working on a coop project for it. As to JK2 though, that is probably a long way off unless some people started working on it to help. I imagine you could play the JK2 maps through OJP in JA. Convoluted, but it might work!