Naveen, Sorry I missed your question. I often paint the bearing caps while still on the axle, in the truck. So no you don't have to take them, but you can take them off just the axle if careful.
Realize that the more you take the bearing caps off and put them back on, In my experience, I think it enlarges the hole so they may tend to work themselves off the axle, so put a dab of glue inside the hole of the bearing cap often helps reduces the likelihood of the bearing cap working itself off the axle.
