Yes. Private Email Relay addresses return the same “valid” result as any other valid email address.
It is important to remember, though, that validating a Private Email Relay address only means that the relay address has been validated, not the original address it forwards to. There is no way to validate that original email address without knowing it.
A user may toggle a Private Email Relay address on or off at any time, causing the validated Private Email Relay address to immediately return an “invalid” result if disabled.
If a user registers for an account with you using a Private Email Relay address and later disables that address, the user may need to create a new account with you.