As well as the Reclusiarch/Chaplain. It has the same text, but they can only have 1. The Captain is an exception, but as stated...you can only shoot a single weapon, so you are shooting yourself in the face if you replace both. Which is why I always tell people that ask this question that it's 1 or the other, depending on which you choose to take. More as a guide to let people know that you are basically wasting points in trying to kit a captain out with weapons that he cant use. Sure..you can take 2 combi-Meltas and have 2 Melta shots with him on 2 separate turns..but why pay the points for a 1 shot gun when those points can be better spent else where..?
I guess if you WANT to spend points there, you theoretically CAN do it..but..it's a waste..
EDIT: Actually, upon looking at the Codex, no. You can't. The basic Wargear options list specifically says Boltgun OR Bolt Pistol, not both. The wording is correct in the options, because it depends on what you choose to take as his basic ranged weapon. You have to choose one or the other, not both.