There should be a special reaction if you bring a tame Lobh-Se to Elpuri's level. Probably a fullscreen message about the two of them first setting an eye on each other and then an instant spark - they fall in love on the first sight, two horrible and horribly lonely monsters. Then the player is presented with a [Y/n] prompt whether he will allow them to remain together. If the player agrees, both Elpuri and Lobh-Se are moved to a neutral team.
This would be a pretty cool and heart-warming story, IMHO.

And not really game-breaking or overpowered by making the GC boss neutral, because you a) need to get tame Lobh-Se and bring her all the way to Dark Level and b) won't kill Elpuri, thus not getting his head and preventing you from Freedom ending unless you afterwards fight both Lobh-Se and Elpuri to get the head. However, you could use it to cicrumvent Elpuri and go directly down to Oree, but then you need to fear the lower GC more than Elpuri, really.