Some landlords screen tenants closely, to make sure they seem responsible and have decent credit. Getting rent paid regularly can make the difference in making your payments on the mortgage yourself, if you are not a large property owner. Allowing someone to sublet without checking out the subletter is risky- what if the person stops paying rent, or breaks things on purpose. Who knows?

My advice is to ask the landlord their thoughts. If the person taking over the room is willing to have a credit check, meet the landlord, and sign a new lease, at least for the time the current lease has left, that should assuage any concern.