I've never heard of this. They may ask on some form, but I've never seen a requirement to meet a minimum.
Which liveaboard was this?
Sorry, I've been online a LOT in the last few days reading & researching different locations, diff. liveaboards, etc., so I can't recall specifically which LOBs (plural, because it was def. more than one or two) stated that divers were required to have a min. # of logged dives. It was most likely LOB based out of the Red Sea or perhaps Komodo, as those are the two places I've spent the most time reading about.
Regardless, I wasn't overly-worried about this before, but I thought it was worth asking others about, and now I'm even less concerned. That said, if I booked a trip on a LOB who's literature stated that they required a min. # of logged dives, as Scubadada suggested, I'd be sure to address the issue and make certain it wasn't going to be a problem before making payment.