under OH divorce law can my husband file for legal separation while we are going through a foreclosure of our house

He certainly could. The only thing a divorce may potentially effect is distribution of property (if there's any equity in the property, and there's any residual after repo. sale...which is unlikely). Additionally, if there is any amount owed via judgment from foreclosure, the divorce decree could establish who would be liable for that. Nothing in a foreclosure would prohibit divorce though.