It is compatible - the motherboard is simply older than the Phenom IIs so they don't appear in its list. The only time you'll ever have a compatibility issue with motherboards and processors on the same socket (AM2+ in this case) is if the motherboard can't provide enough power!
HOWEVER
If you can stretch an extra £12 get the
Gigabyte GA-MA790X-UD4 instead - it has the newer (and much better) SB750 southbridge chip. it will be £12 well spent!
If your budget doesn't have any stretch consider getting the more expensive motherboard with a Phenom II X3 720 instead - it's quite a bit cheaper, a very good performer in its own right, and it is *possible* to unlock the 4th core (thanks to ACC in the SB750 chip) so you could end up with the equivalent of the X4 920 anyway!