You can send PMs to other people to talk about them, but you have to spend actions to make it official. You can spend your secret action on this, but if one member of the alliance doesn't make it their secret action, you risk being exposed.
You may make an alliance with multiple people at once, or send diplomats to multiple countries at once with a similar purpose.
There are still about... five(?) players that still need to fill in most of their country things, so one or more could very well fill their country with non-humans.
Having a race different from your neighbours will make it harder to do cultural assimilation projects, which makes taking total control over a country with a different race harder. Basically this means having a non-human race can work as a defense mechanism of sorts, as people may not want the hassle of taking over such a region and deal with rioting that may ensue.
Yes, it's kind of gaming the system, but it results in racial diversity, so is that a bad thing?
(Also, don't worry. I regularly game irl with WaylanderX and he usually has terrible luck. I'm sure the tables will turn for you later on, especially if you play cleverly.)