You can hunt CRP land all you want. The only thing you can's do is mow it at certain times of year (but you do have to mow it - I believe every 3 yrs.); plow it (not sure but you might be able to plow to establish better "habitat"); you can't develop it; and if you sell it the CRP goes with the property.
I even believe you can establish a food plot on the CRP ground - sometimes they will even cost-share it. Normally they look to creat warm season grass habitat for pheasants and other ground nesting birds.