Currently the "UserId" info is stripped from the
Votes table for "BountyStart" and "BountyClose" vote types (i.e. for
VoteTypeId=9 respectively, check an example). Since this information is public on the SO (can be seen in question rev. history and in user profile as well) it would be nice to have it also available in the Data Dump.
@Those who upvoted this request: you may also like the related one Add bounty details to Data Dump for "BountyStart" event.
When both of these requests got implemented we'll be able to write sophisticated queries determining top bounty starters and winners, altruists and sponsors etc. (and yeah, we could propose some new badges to reward them). So if you like it, support it!