Not at all! While HelloSign is heavily integrated with Google and Gmail, you do not have to use Gmail to use HelloSign.
If you send your clients a signature request via HelloSign, they simply need to have a valid email address and internet connection. That's it!
Only our HelloSign for Gmail plugin and Google Drive and Docs integrations require a Gmail account, but you do not need to use those features to use HelloSign. Those are just added integrations for those using Gmail.