It's unlikely anyone will take this up as it's a pretty niche request, but why not.
So, Pierson's Puppeteers (https://en.wikipedia.org/wiki/Pierson's_Puppeteers) are a race of intelligent herbivorous aliens from Larry Niven's Known Space series. Details are on the Wiki page for a rough idea of what they look like and how they act.
I'd like to see them as rare wanderers/escape pod survivors that can join or be recruited to the colony. Rather than just giving regular traits and skills to some new art, they'd have features unique to their race that would be useful, such as a "tasp" which is a device they use to pacify other individuals and a powerful melee which they only use purely defensively (like when cornered) and never as a direct attack. Of course, they have flaws, like commonly being perceived as cowards and pacifists, so they'd generally be non-violent (except for the aforementioned melee), they eat no meat, only plants but don't have as much of an issue with nutrient paste as regular colonists.
Anatomically, they're quite different from most other Rimworld creatures. They have three legs (two front, one rear) and two "heads" with a mouth and an eye on each which they use for manipulation and as such have hands or arms. The brain being in the main body under a thick mop of hair. I think this would make for quite an interesting colonist when it comes to taking damage as it could lose a head and leg and still be able to move around and function. Maybe not as efficiently as a human, but more so than a human missing a head and a leg.
I'm not really one for using existing IP's but I'm a bit of a Niven fan so I thought it was worth a shot.
while you are at it, why not add Kzin?
ie wild CARNIVOROUS inteligent plains CATS(lions that walk upright, also from known space by larry niven