I would strongly advise against cluttering up your suspensions with a huge list of spammers who are never going to be unsuspended.
Suspensions are for users that can, at least in theory, be reformed. They are meant to be temporary, not permanent and ever growing.
If you want a firing squad (and you probably do), use that and just log the email, ip and username if needed – though I am EXTREMELY dubious of the value of tracking username based on my experience moderating / running Stack Overflow, which has millions of users.
(Note that Discourse automatically tracks the email and IP of spammers you remove, and blacklists them. Extending that to blacklist user names too is possible… but again… I am very dubious of the value there. )