SELinux is not related to FIPS 140-2. You can use SELinux as part of a FIPS-compliant product; you can equally not use SELinux as part of a FIPS-compliant product. Whether it's a good idea to use SELinux depends on the complexity of your product and on how much work has already been done (by you or others) in defining relevant SELinux policies.
FIPS 140 level 2 requires at least role-based authentication. User authentication, as provided by the most basic Linux system, is sufficient. Role-based authentication means that you're allowed to have shared accounts (e.g. a direct login to root), but you don't have to use any shared accounts.