My husband's ect has made him lose some cognitive abilities but his doctors are strongly recommending it again, is it safe?

It may not be safe.: Ect, medically safe, can help with severe depression, manic psychotic breaks that don't yield to medication and schizophrenic psychotic breaks that also do not respond to medication. Unfortunately memory loss can occur. Not often permanent , it can disable one, for months and sometimes years, in work function & every day living. Rare permanent memory loss can occur especially in elderly folks.

Yes: Ect is safe. It could be the condition that the ECT is treating that caused the cognitive lose. Was the lose severe? Once is a coincidence, but twice is a pattern.