No they are not immune to it.
The thing is, if you want to keep fighting a faction you maxed your influence with, making them immune to your slaaneshi attrition would help them right ?

However you can use an other mod which provide attrition immunition from the corruption of the master (and also spreads it)
This mod is this one : Vassal Corruption Immunity And Spread (VCIAS)
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2862340751

small question but since the factions spread the corruption (aka on the ordertide side) does that mean they are immune to it?