There’s a reference on this thread to a hacked account regaining access in 2020 using and signed message from an ETH address instead of a BTC address. On the other hand, I have been reading through a bunch of cases where people only had an ETH address and apparently they did not succeed in recovering their account.

My guess (not a known fact) is that it could be used in some exceptional cases, on a case by case basis, but not as part of the usual procedure where only PGP and BTC signatures are explicitly mentioned.