For the record, I have had 2 coyotes come charging at my turkey decoy while calling this season. I use turkey decoys in the winter as well for coyotes, as ocasionally you see a kill and its is a food source for them.
I would argue that if you are on the way out of the bush at 7:01 pm, that there is no prejudice for a CO to charge you hunting turkeys with an uncased gun-remember, you are enroute to your vehicle. Plus, as turkeys are wary, fickle creatures (e.g. they bolt at 300 yds because they SEE you),you couldn't actually be hunting turkeys by walking around in the bush (vs. sitting camoflagued and motionless), could you...?
Can you use a digital call with a turkey vocalizations when you're hunting coyote? Again, I think a CO would have a hard case proving you weren't hunting coyotes. If you are after varmints, then would you use a 1 3/4 oz turkey load-probably not, so if you are interested in varmints, I would use an appropriate load.
I don't recall anything in the regulations about cased gun, however I could be wrong. If it is stated, well we all know the answer then...