Sure, it would be great to see death messages turned off in Buildbox, but then you'll still be able to see the players, who are pvp'ing, most likely say "Hey! You're cheating!", "Stop throwing splash potions at me!", "What are you even doing?!" etc.
And besides that, the core aspect of Buildbox is that it's a creative server, it shouldn't be used for PvP'ing UNLESS (I'm sure that this could be open for interpretation) someone is using custom weapons to test it out for their map -- which usually happens 5% of the time from what I've seen.
Then again, I can see the fun in making your own custom weapon and using it on players or animals. So overall, I think that death messages should be turned off and PvP'ers should be in RP chat when they're fighting.
As a side note, I find it concerning that a couple of Builder ranked players are PvPing in Buildbox.