Well, bottom line is, the OP who put them up didn't call them OMB's...just 'famous musicians', and to be fair, many of them play like they are used to comping for real bands, just having fun with an arranger for the first time. None of them do much other than change variations and call up the odd ending. But chops....?

Yes, indeed!

Mad skills on that #1 'Have you met Miss Jones?', the Rogers and Hart standard.

However, nobody is claiming these guys actually go out and GIG like that. So that OMB title still lays open!