What do you mean with "maintain"?
a) Have an OBI Server run more than 1 RPD? No.
b) Just HAVE multiple ROD and switch them out? Sure.
c) Merge the content of mutliple RPD into one big one? Sure.
Of course you can ... by hand!
Just making sure to remember to merge all of them before to deploy the RPD. You can perfectly automate these steps and so end up with "virtually" multiple RPD on your OBIEE server.