No, this is a lower level of sponsorship than jersey or stadium sponsor. They don't even have a proper stadium (but that's another story). That said, I'm sure you will see some advertising for RC around the stadium.
I could go into a lot more detail as I'm a huge MLS (and football) fan, but I'll just say yes, Messi is bringing A LOT of eyeballs to his matches. Apple TV holds the international rights to MLS and part of Messi's contract is getting a % of revenue from all new Apple TV subscribers from the day he signed.
Will this do anything significant for RC? No idea but it's probably not a bad marketing decision as I doubt it cost them very much in the grand scheme of things.
FWIW, my avatar is an MLS crest for my local club (Orlando City).