The whole point of Loco carriers was to keep costs down, so they have no interline agreements for staff or duty travel nor any agreements with legacy airlines for through ticketing/interlining baggage etc
Thus any staff travel on Loco is for in-house staff only.
The days of everyone helping each other out on staff travel and/or mutual aid is dwindling but some carriers are still very nice to staff - In the main BA TUI and Virgin still look after staff I find.