Nah, you needz ta git you some pointy ears. Dey'ze would make great grotz for the boyz to kill.
Well...
The only Eldar that Orks would encounter would be aspect warriors, who would find some way of
either killing themselves or escaping. Or if a Dark Eldar raiding party attacked an Imperial world that the Orks have taken over. But then the enslaved Dark Eldar would die from not eating a 1000 souls a day.
Well I do suppose the Orks could get lucky enough to occupy one of the Maiden Worlds of the Eldar, but then again you do have the Biel Tan Craftworld constantly trying to defend the Maiden Worlds and blow up Ork spacecraft before they land on occupied territory. But then again Orks do get lucky a lot of the time, just talk to my SAG mek.
Ork enslaving humans, yeah I can see that, I love that. Orks enslaving Kroot, well in the fluff didn't they until the Kroot rebelled? Orks enslaving Tau, well only if your Ork army is based in the Eastern Fringe, but yeah I can see that without any problem.
What about Orks enslaving Nidz or other strange beasts like the Clawed Fiend of the Donobian Sector or the Hrud which were only shown in a small pic of the 3rd Edition dex.
Even better if you can get your hands on some squats! They'd make the perfect Ork slaves, they're already as small as the grots.
Peace
~OD