Hello S3rverSavvs,   Dell has not validated it as it is non-Dell part. I'm sorry I don't have any guidance for you on that drive.   Hopefully anyone in the community that has tried it can share their experience.   I do see we have this one available for the R660 and if you contact Sales they may be able to quote you others: Dell 1.6TB, Enterprise, NVMe, Mixed Use Drive, U.2, Gen4 with Carrier [URL]  
Although it wouldn't have Dell's firmware on it, would the Micron 9400 NVMe SSD be compatible with the R660?  Thank you!
R660 Server with Micron SSD