It looks like, from the wording on Gerard's special ability, that he can hire more than one mercenary per beat if he's got the available gold. It's also not quite clear if you not only can buy the mercenary during ante but also ante the mercenary's special ability in the same beat. There are only the 3 mercenaries that operate this way but...
You can buy more than 1 a beat, I think. Did I say otherwise in the video?
Also, you can hire then pay the Gunsliner, Mage, and Heavy Knight in the same beat.