If you have an Intalink branded ticket it's usually the case that you can show it with the barcode folded away and the driver will recognise the brand and accept it, as per the conditions of the ticket.I feel like using an e-ticket and trying to scan it is a recipe for disaster on the majority of buses.
For most drivers a failed scan= invalid, and they are much less likely to accept it.
If you show them a paper ticket, after a bit of conversation which normally is along the lines of 'that's a rail ticket'; 'no its not, it's a plusbus', the vast majority will just let you on.
If you scan it or show them it with the barcode visible they usually won't accept it without it being scanned. This will decline for operators other than the one on whose bus it was purchased, and the driver will then tell you it isn't valid.
Usually bus drivers fall into two categories: the first accepts whatever is shown to them, focusing far more on driving safely, keeping to time, and that passengers are going the right way, than about whether someone has underpaid. They may query where someone wants to go to or something like an unacivated mobile ticket, but they won't delay the bus to do so. The second automatically says no to something they don't recognise, and tries to charge fares in any circumstances they think they can. They will never, ever admit to having been wrong, and ironically they're usually more likely to be wrong in the first place as a result of this negative attitude.
There's a small contingent of drivers who fall in between and actually know what all of the tickets are that are valid on their service, or in the unlikely event of a surprise they will pass tickets they don't recognise and check later. There's at least a few drivers in this category who could be reading this very thread.