On the one hand, comment votes for the commitment phase would be rather harmless in terms of mechanical effect. If we consider them like standard comment votes, there's no reputation gain or anything else, so it's not like there will be anything problematic. It can be seen as a nice gesture of appreciation, too.
On the other hand, there's a lot less effect for voting on commitment comments. The current comment voting system has a primary effect of ensuring the visibility of the comment. It basically states "This comment is great enough to be distinguished". So it works well in the comment systems on posts and proposals because we will be rating the comments. Commitment comments, on the other hand, are not hidden, so there is no need to highlight any of them.
Which means that the only effect of such voting will be a ranked number in front of that user's commitment comment, subsequently implying that commitment comments should be ranked, that there is such thing that someone's commitment comment is more valuable than others. Considering that commitment comments are tied much closer to the user than other forms of contribution (as the commitment comment is an expression of the act of commitment, which is itself an act of that user's devotion), this subsequently implies that the votes will rank the users. Which means that we would be putting value on the reason that people are committing to a site. Is committing because "I believe a web application specific site is sorely needed." more or less important than committing because "I love creating web applications"? Do we want to encourage people to come only for the reasons that are most popular?
It doesn't matter whether you are intending this kind of rating, the fact is that people will read this kind of system as having the users rate each other, which is against the spirit of the system (vote on content, not people). If you want the votes to just be meaningless expressions of amusement over the content of a user's commitment comment, then the votes are just that - meaningless, and a waste of time to implement.