@spikesguides@BLThompson88 Louisiana State University literally has two Indian (feather) burial mounds in the middle of it. It's a couple blocks over from the tiger cage.
If you're sticking to canon, I would say no, because it's fundamental to the SoB that they are female. Having someone that could potentially violate the Decree Passive would invite severe problems from other factions in the Imperium, or even threaten the existence of the Adepta Sororitas. The Penitent Engine isn't just for torture, it's also an execution device.
If I recall correctly, your main character is a newbie in the Inquisition, right? They could find the futa Sister in the Engine and rescue her, and she could be accepted into the Inquisitor's retinue (maybe even be declared a Sanctioned Abhuman), but she wouldn't be allowed back into the AS or SoB.
However, this is a fan work and you aren't obligated to stick strictly to canon. There are plenty of people who make futa 40k art. I think there's one person who posts on Warhammer Smut that has the "Sisters of the Unbending Rod" or something like that.