It should be OK. I would recommend going to Mr Malty and checking out the pitching from slurry functionality. That should help you figure out how much you'll need for proper pitching rates.
IMO, the 2 things to worry about with pitching on yeast cakes are these:
1) Pitching rates can be tricky. Too much yeast initially can affect the flavor profile, as esters are created during the yeast's reproductive phase. If there is too much yeast, they won't need to reproduce and they won't create these esters.
2) Depending on what your first beer was, some of the characteristics (hop profile, color, etc.) can and will be inherited by the second beer. Conventional wisdom suggests to move from a lighter to a darker beer. So, pitch a brown ale or a porter on the yeast cake of a pale ale, or something similar.
Both of these issues can be relieved by washing your yeast. It's fairly easy, and you can reuse the yeast on almost any future beer. Up to 3-4 generations, your yeast should be fairly mutation-free.
The wheat might affect the IPA, but I would do it, if it were me. Again, check out that pitching rate calculator to see if you need to reach in there with a sanitized ladle and pull out some of the yeast.