Same applies to me as well, albeit it wasn't a replacement bus (but have been in the same instance recently). The last Glasgow QS to Dundee service yesterday I was on consisted of 2 x 170s, and not once did the guard bother to check any tickets, and not once did he attemped to change units to check them further, as guards normally do. No wonder Abellio tried to introduce certain measures of which I won't mention....
It's none of my business to get involved in what other folk were doing. As far as I'm concerned isn't it up to the guard to check the toilets on his way through the train? Also, the catering crew were through a couple of times and should've checked for a valid ticket before serving complementaries, so I'd of assumed they'd of taken care of it. They wouldn't have even gotten onto the train had barriers been installed across platforms 1 and 2 at Glasgow Central and at Carlisle.