Can rotary tool bits be used with a drill

Most driver bit sets come with a 1/4" square drive adapter (my small Milwaukee set also came with a 3/8" drive as well, though I don't know if that's common). With that one bit, your driver is instantly almost exactly the same as a 1/4" impact wrench. You'd have to look at torque specs to see if the models you're considering are comparable, but I bet they are. Those little impact drivers have come a long way -- battery life is great and the torque is hard to believe.

I'd only consider a square drive impact wrench for heavier automotive (or other mechanical) use, and only in a larger size like 1/2" so it can provide some real help in removing tough fasteners.

Not really. I did this and regretted it.

The problem is that the rotary hammers that are worth it are very heavy and overbuilt (the larger Bosch SDS series etc.). They make fantastic rotary hammers but are too heavy for use as a drill for extended use unless you have really beefy forearms. In this scenario, you should get a 18v cordless drill for when you want to drill.

Then there are very lightweight rotary hammers (such as from Harbor Freight) where the rotary hammer action is extremely weak. These do a good job as drills but not as rotary hammers.