yes, to a certain extent. There appears to be a max limit on how much XP you can get from a single kill, your heroes of course get 5x as much xp as you do if they are below your level.
You can stack them, but using a double or a triple XP on top of the bounty yeilds the same amount of XP, even for the bosses. This has been reported as a possible bug and is still under investigation by ANET.
