I can see your argument, though, for the purposes of my games, I disagree with it. Without mentioning some other form of transfer, I think "blood loss" can be, and should be, ruled to occur as a result of an actual wound, which would require actual damage. If the blade were to magically suck blood from the body without any wound required, I think there'd be a mechanical touch attack option (as is, in fact, the case with a Rapier of Puncturing.) As there is not, and the flavor text mentions blood loss, it seems clear to me that Wounding does not function if a wound isn't made.