Yes, I'm not saying they are going to cause him denial. I also think that the ECO prejudice associated with jobseekers' benefits might not exist with disability. Also, as you say, the rest of your application was solid, so they had no basis on which to deny you even if they wanted to. And just because it wasn't an issue in that your visa was granted, you don't know whether they were more critical of your finances than they would've been otherwise (fair or not).
All I'm saying is that it's better to ensure you have a solid case if you're on benefits rather than rely on the goodwill/justice of the ECO. Just because he is entitled to benefits and they shouldn't hold this against him and look for holes in his case because of it, doesn't mean they won't. As Vicky has said, wrt non-visa nationals. But also as Vicky has said, they'll be forgiving as he's American, and so I'm just being 'visa-cautious'-- it's like being 'overly-cautious', but to a degree approaching paranoia. Happens whenever I start thinking about preparing visa applications. ;-)
Di