They would be outmatched by the sure numbers but they would be a good power house with fusions fighting titans and such, probably treated like a minor annoyance like the tau.>eldar
The eldar would probably be interested with them and may have had some hand in their creating but that would be up to the writers, odds are craftworlders would use them as pawns like everyone else, while Deldar would have a fun time testing the limits of their pain receptors.>orks
Orks would probably be avoided by the gems because they are a force of nature that doesn't go away easily, orks would probably target them to use as shiny gubbinz.>tyranids
They would eat them like everything else good source of vitamins.>necrons
Necrons would be mixed some would try to destroy them for being in their territory others would study them for the history books, the gems would probably avoid them like the plague as their weapons would easily shatter them on a molecular level.>tau
They would try to recruit them, when that doesn't work than large amounts of mechs vs fusions.>chaos
Corrupted gems would probably be possible is rebellion is possible, and odds are the gods would try it. and the gems if they understand the threat would have a shoot on sight policy.