Not sure about that. I would just make sure and read all of the fine print so they can't get you on a technicality.
Personally, I would think as long as the email addresses are different and the credit cards paying for the offers are different then there won't be any problems.
Also, I think one thing that would be good is to make sure the referrals are all done from different computers (different IP addresses). This might not matter, but I just didn't want to leave anything to chance!