Sounds like a good way to have an open bar in reality, while not violating the venue's policies. I'm impressed the venue allowed it, though, since it seems like it would be more work for them (someone would have to total up every individual drink).
Remember the thread from a while ago, where the couple wanted only a limited alcohol selection (which the HC would pay for), but the venue insisted that they be able to display all their alcohol selection and would make a drink for cash upon request? So even though the couple had no intention of having a cash bar, if they went with this venue it was either pay for a completely open bar themselves, or pay for limited alcohol with a sort of "black market" cash bar on the side. I realize some people/places feel like they're strapped for venues, but just on principle I'd rather have my reception somewhere else, than have it somewhere that forced me to do something I really didn't want to.