Hmmm, let's see, we can't with our closest cousin the chimp with a mere 3-5% difference in DNA. How likely is it we find some alien from another galaxy evolving in a completely different environment being biologically compatible with we humans? I'd estimate the probability around 0%. In fact the probability is higher we could procreate with any lifeform on Earth before a species from another world.
This is something that was always hilarious about Star Trek, where some episodes had two species native to a single planet be unable to breed with each other, yet countless other episodes showed species from the other side of the galaxy to each other be capable of it.
(Even when DS9 and Enterprise later suggested genetic manipulation was required, it still didn't handwave the umpteen other examples)
Intergalactic hybrids would be probably be a bad route to take.
The only way that it could perhaps work is if the alien species were either to reproduce like the Asari (finding another species like that would probably be a stretch though), or one capable of biologically transforming themselves into another species, so both are compatible with each other.
The idea of an alien species who rather than terraforming a planet to colonise, instead bioforms themselves to suit the environment is actually a rather intriguing notion. If they had the advanced technology to pull off such a feat, wouldn't be outside the possibility they might program it to replicate Human/Turian/Salarian physiology?
Could even be a source of conflict, with people becoming paranoid whether the person next to them isn't actually a "changeling" or "pod person"?