Not at all.
There is a P3 cameo reference in P4. It doesn't matter, though, as it's not crucial at all in understanding the storyline of P4.
There is one cutscene involving the ultimate secret boss of P4 with heavy reference to P3, but that's the only one, I think...
For your entertainment:
http://ningin.com/mediastream/item:show/2008/11/21/megaman-movie-official-trailer/







