It will probably be compatible so long as it doesn't contain anything that was removed or seriously changed in the next version. (For instance, a Maceman would break a map if loaded after these unis were changed to Champions.) If so, you can edit those things out in notepad, although that could take a lot of time and might be beyond your skill. (I've never really tried, so I don't know how hard it is)
I'm not sure, but is is quite possible that the BtS 3.17 patch would make any maps from earlier versions incompatible.