[quote=@Cyclone]
... Secondly, do white giants attack urtelem? If white giants ignore urtelem then I think that the ogres are good, whereas if they attack urtelem then I would presume that the ogres would only have to deal with one or the other in any given area.
[/quote]

The reason that urtelem were deemed safe from white giants is because Urtelem could duck underground a short distance to hide while a giant strolled by. The giants aren't too clever, so they normally don't pursue creatures they can't detect with their limited senses.