Yeah, you can always get a bus pretty easy to a resort for a dinner ADR. However, that may not be the easiest and/or fastest way.
For example, if you are at Magic Kingdom and are eating at Chef Mickey's, you would want to take the monorail to the Contemporary or just walk over there. Same with any of the monorail resorts (Grand Floridian, Polynesian, Contemporary) from either Epcot or Magic Kingdom. For other parks, it might be better to take a boat.
It really just kind of depends. If you know exactly which park you will be at and what resort you are eating at, people on here will definitely be able to tell you the easiest way to get to the resort for dinner.
But the simple answer is that it is not a problem at all.