It's all matchup based.
Some teams are more athletic and play off of it instead of size. Vitor is new and learning the defensive schemes. He also is not a finesse player, therefore he needs to be against another banger or two when possible. He will need some more work before he is an everyday center or even an everyday backup center that can play against different types of lineups.
I also fully subscribe to the theory that Brad Stevens 'threw him out there' to 'see what he had' in those first two games. Likely Danny was happy about this and may have suggested it even. They both know we have a lot of unknowns on this roster as far as how guys will perform at the NBA level and how they will play together.
If Humphries is trade bait, and I believe he is, then he must be played some to establish value. Same with Bass, Lee, Wallace, Crawford and any other player Danny may make available. Likewise, we also have to play our young players like Vitor and Olynyk to see what we have.
We would have never seen this type of audition with Doc Rivers IMO. I think Danny and Brad know we dont have a shot at the playoffs, even after winning a couple of games, and they dont have a problem with an experiment or two that may cost us a couple of wins.
In answer to the OP, yes at this stage of his career he is but not going forward.