You have regular user's that use your website/services, they can login to mainsite1, then you have developers, that can not login to mainsite1, but can login to developercenter1.
1) Do you store every type of users into 1 large USER table then assign different roles?
or
2) Do you create a completely separate table just for developer's? since they are both completely different user's using two different sites?
id use a roles based system as having 2 similar data structures may be a bad idea going forward - if you change one and not the other then you may have issues
It's probably appropriate to centralise the logins, then add roles, and then link special properties for each group through a related table.
So yes, I'd assign roles, and keep login centralised (this means it can be one codebase to do the login, which is good).