I understand your question.
According to Treasury Board, and according to the program arrangement or agreement that was signed between the Department of National Defence and Veterans Affairs Canada in 2006, re-signed in 2012, Treasury Board's agreement on this issue is that because this is the employer-sponsored disability program, the SISIP LTD program is first payer.
So if anyone is eligible for those benefits, they must, or they should, come to SISIP first.