Yes. Signal has perfect forward secrecy. There's no way any government could compel them to release private chat information: they are literally unable to do so.
Even so, a government could still block them until they realized it's futile (or something). The end effect is in their favor: users to move to other platforms that are not as secure.
WhatsApp does/might (who knows, they are not transparent about it and it is closed source) employ the same end-to-end encrypted protocol as Signal does (for some users):
