I have a Synology NAS, and the account you create with them is separate from the ones you create on the device. They couldn’t log into my device. Their account allows for easy integration with their stuff like the dynamic dns or other outside services. I like it because if my internet goes down, I get an email saying they lost connection, which is great for diagnostics.

If I set up my router to block all traffic to them, it would not prevent me from using the device.