In answer to your original question, you can joint end grain. Make a short pass, about 1/2" or so on one side then rotate the board and make the full pass. The first 1/2" pass is to prevent chipout that would occur if you just did it in one pass. You also want to make light cuts, say about 1/16" at a time. But, as others have mentioned, a sled on a tablesaw with a nice sharp 60-80 tooth blade would eliminate the need for using a jointer.
You could also use a straight bit in your router with a guide board clamped to the door as a guide. But again, you'd have chipout at the end of the pass so if you use this method, make the door a little wider than final dimension, clean up the end grain, then cut the door to final width, cutting away the chipout.
Lots of ways to do this, just depends on what tools you have. Good luck.