I've seen some líberos play as OH in Brazilian league this year (Gabi from Sesc and Kika from Osasco, for example) but I think they've been listing only 13 players.
well, technically they're not OH, they're "regular" players. they often come in to serve/defend for an MB, and when they lose the serve, they still stay to receive (and an OH/OPP goes out)... but when they get to the net, they get subbed again. that is very common all over.