They don't need to hide allomantic abilities, since the y would be able to control inquisitors.
For the lord ruler, allomantic pulling is not the only way: you can cut his arms, and with a surprise strike it wouldn't be so impossible (kel keeps him busy with enhanced pulls/pushes, and he is very good with them, vin attaks from behind with enhanced pewter).
I guess that most likley they would lose, but I expect that they might have a chance