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.
AFAIK the rule is either 12 players with 1 libero (but also 2 allowed), but as soon as more than 12 players are registered it's obligatory to have 2 liberos.