I think, that you imagine problem, which does not exists

. I consider those options quite useless. Why should i add restriction to single subscribe option, if other one don't have those?
And yes, this mod uses mailqueue, according to general vb settings.
By the way, 3.8 mod doesn't use mailqueue because of programming bug. I haven't found vbmail_start() / vbmail_end() there. That causes huge count of SQL requests, if you have lot of forum subscribers.