^^ The answer is yes.
Although I expect there to be an un-official rule too with Virgin and London Midland.
Virgin pays better and there is usually overtime (RDW - Rest Day Work) available. But then their route is restricted now. A Govia pass (IE, London Midland's equivalent of Virgin's travel pass) would give you better options for travelling around further, but their trains are slower.
I looked at the roles, but the lack of details put me off somewhat. Then again, it could be a good position to get your foot in the door so to speak, then move on. But some TOC's prefer not to take on people from different TOC's as they want to train the new people their own way, or so I heard.
All depends where you live, what you really want and if you plan to use the extra stuff you get with the job.