If the rogues forces are the defenders in a rogue region, why not? Rogue forces will use your siege engines if you are both attackers going against fortifications. I always found it kinda funny when you share your siege engines with an undead horde.
There had been some battles where monsters/undead forces actually used SEs and did something your usual TLs couldn't accomplish. I still remember a battle where 1.4k undead horde wreaked havoc while my own unit got pushed out of the wall...
