I don't think house moms/directors are mandatory, b/c in all of our canadian chapters (where i'm from) do not have a house mother. i was house manager for my chapter, but i was active at the time. however, i know alot of our chapters in the states do have house mothers. i think it may be different on every campus, and maybe have to do with the size of the chapter?
i agree with 33girl, if we did no one would want to live in the house!! out of the 7 sororities on our campus, i believe 4 or 5 have house mothers. all of the house mothers are alumnae from their respective chapter. the house that is our biggest competition during rush just got one this semester and i (as well as they) think that it will have a negative impact on rush for them.
i'm not saying house mothers are bad, but just not suitable for our campus.