Personally I would be very wary of letting another DBA administer your environments. How sensitive is your data, how complex is your environments, will it always be the same person(s) as they will need accounts with the relevant privilages.

You also have no idea how good or bad they may be, would employing a part time DBA not be an option, or a graduate and train them up? A graduates salary would be significantly lower and you could possibly bring them in on a shared role as a developer \ dba.