IMMHO, I would think that a DNR Warden would need to have some reasonable suspicion that something illegal was going on. For example, I don't think a warden would be driving down the road as think "that's a nice 40, I'm going to take a walk in there to see if anybody is baiting deer." However, if a warden sees a person haul sacks of corn into a 40, he would probably go and check it out. (assuming baiting is illegal in that county.) If he had some evidence (or maybe a complaint) that something was amiss, investigation is valid, at least that's how I read the statutes. On public land, the warden IS the caretaker and will investigate anything.
Since hunting is a privilege and requires a license, a warden has the power to check for your license. What I am not sure of is when a warden sees a hunter 300 yds away on private property, would he think that he can get out of his vehicle, walk across your land, and check your license or your gun, or whatever. (Assuming of course that the warden has the ambition to do that.) If he saw you on the road or near your car, he might stop and check.
I don't think a warden could go looking for a problem, but would certainly investigate a problem or potential problem.
Of course, this is my opinion. Take it for what it is worth. (ya, I know, not much)