system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] How do Borg assimilate non-humaniod species and other species which needs very special living conditions into the Hive?
gpt
Borg drones can apparently survive in highly inhospitable conditions. In First Contact, we see human Borg drones operate on the outside of the Enterprise without apparent extra equipment. So the cybernetic augmentation can probably keep most drones functional in the same environment.

Otherwise, they might assimilate them by planet where those living conditions are met. If they can benefit the Collective without ever stepping on a vessel, then why not assimilate them? Or if they are beneficial on Borg vessels, then there might be specialised areas for them. 
After all, Federation vessels apparently also had quarters for non-humanoid crew members. While never shown, it's occasionally mentioned how the Enterprise in Next Generation has a few whales and dolphins as crew members.

The Borg might have similar areas on their vessels, planets and structures.

Else, if a species is  more trouble than it's worth, they'd probably just ignore them.