I’d like to know if I connect my Trezor wallet to a MetaMask instance or if I import my seed phrase to another client I’ll be able to access my hidden wallet.
You can. Access is fully possible as long as other apps support the passphrase feature.
ledger also supports passphrases. In software wallets, I know that Mycelium can independently support setting a passphrase.
MM seems to only have the option to enter a passphrase when connecting to a hardware wallet.