This is the wrong section, er, sorta?
You might wanna check the
Squid Locator, but to my knowledge, no matchmaking hub discord server exists.
This was just a quick search of that board, anyone please correct me if I am wrong.
I don't know the viability of a matchmaking discord server, only because most individual squads have their own servers, and contact each other both here and across one another's servers.
A matchmaking hub may not see the most use in that regard, but you could grow it yourself, maybe something for free agent squids not looking to squad up, but just looking for fun folks to play with now and then.
As it stands, there are large casual squad servers that do that already; maybe create your own hub and work in partnership with them to promote said hub server/service? It's nice, the idea of friendly new folks to play with, with no strings attached for squashing or competitive ranking.