I don’t think so. The key cases are Menear and R(H) 9/04.
In Menear, the Council wanted to treat two people as a couple; one of them had capital from the proceeds of selling his house and the other was on IS. The Council decided that the couple had capital in excess of the limit for HB and disallowed the claim. Mrs Menear won the appeal on a very limited technicality:- the Council was entitled to treat them as a couple, and it was correct to aggregate all their income and capital, but the structure of the HB Regs meant that all the aggregated capital fell to be disregarded because she was on IS. The principle does not work in reverse. This was confirmed in R(H) 9/04 – the claimant and his ex-wife had been treated as a couple for JSA purposes, but the Council was free to decide that they were not a couple.
On the facts described here, the definition of couple in s137 of the Conts and Bens Act seems to fall at the first hurdle – they aren’t part of the same household. They may or may not want to challenge the JSA decision, but that needn’t worry the Council: the Council should make its own s137 decision