If you mass deploy a ship and change races, you can still mass deploy that ship!!!
100% duplicable, just choose a race, click mass deploy on one ship, go back to the mission select window and change your race, then go to a mission and BOOM! You can deploy that ship in mass deploy style!
Result:
Gratuitous Forum Bump!!! This is a major problem and has still not got much attention!
Cliff, fix it!
Good catch, I hadn’t ever thought to do that!
this is soooo exploitable 
I always wanted to field mixed race fleets. Bonus!
while we’re on the topic of mass deploy… it’s a pain in the ass to mass-deploy frigates near cruisers sometimes, since you always end up selecting the cruiser somehow. ugh.
Still not fixed in 1.15…
I’d like to this this as a feature, making mixed fleets has actually turned out to be rather fun, as unbalanced as it can be. Thanks for pointing this out.
I guess I should fix this, although as I suspected, people find it cool.
There should definitely be some thing, story-related or unlockable that lets you employ alien mercenaries…
Fixed for 1.16
What about as mission parameters, something like “may use X% of your points on out-of-faction ships?”
Indeed, as a future feature, it could be pretty good.
You could even have missions allow specific faction mercenaries, permitting you to tie the factions to different geographical locations. Might enhance the richness of the setting.