In the fluff, Ogres are generally employed as mercenaries, as opposed to an army in their own right.
Can I do the same in the tabletop version?
So, it actually depends on the Version you're using. On 6ed et 7ed, mercenary did exist and (at least for 6ed) ogres had a special rules that let them be purchased as mercenary for anyone except Bretonnia. (I do not recall Lizardman beeing able to recruit them, but i've lost my 6ed book..)
Since 8ed, there is no mercenary that exists per se, there is "pacts" you can do with storm of magic (an extension). During End Times, you did not have mercenary but larger army pool. And nowadays Warhammer doesn't even exist.
During the mercenary era, basically, if it wasn't an enemy of Skaven (Like the pirates dwarfs) it could be recruited by them, and if it's not an enemy of the Empire (and even in some cases), Empire can recruit them. These two factions had a lot of mercenaries available, Chaos very less so, Khemri and Vampire counts had a few mercenaries available only for them (but not the same) and for the others, well, it depends.
Hope it helps!