I'm not a spotter, but I am an enthusiast. I'm also a volunteer signalman, guard, controller and so on and so forth on a pretty big heritage railway. I was perfectly candid about this in my interview (the managers definitely not being spotters) and I've got both jobs I applied for within the company, both safety critical operational roles (dispatch and guard). I know plenty of other people in the same situation who have been taken on throughout the company in all sorts of grades from ops to managers to guards to drivers to back office having been honest about it so I would actually say that unless you are a proper obsessive cabbage then it's no bad thing. It's all useful experience, it just requires presenting properly, IE rather than saying I know everything, use it as examples of working to regulations and cash handling, with the added point that you are aware it's best to put it all out of your head when training for your new role.