This is the reverse though, a GBJam entry being entered in the GB Compo.
I think as long as it was made in the timeframe, and can run on real hardware, there shouldn't be a problem. But I'm not a judge, so don't take my word for it.
The big difference between GBJAM and GBCOMPO is that Compo games must actually run on a gameboy/gameboycolor, where GBJam games just have to look like gameboy games.