From my own (unfortunate) experience of direct payment into my bank account I would even go further than the standard rent agreement - make it plain and clear in your contract with the tenant that although rent allowance is being paid directly from the Dept Social Welfare into your account, the contract is between you and the tenant, and any shortfalls in the payment are the responsibility of the tenant and must be paid in full by the tenant. And point it out to them verbally before signing.
That way, if the tenant breaches any Rent Allowance regulations resulting in their payment being suspended, or if there is any messing with red tape, it puts the onus on them to sort it out, and you don't have to listen to any b.s.
I had a major headache with that scenario a couple of years ago. Sorted it out eventualy, but a major headache.