There was a deleted scene that explains it all. Basically Perrin always knew what Mon was up to, and covered for her to the ISB. Sculden owned a broadcast channel that, when ordered, refused to cut the feed to Mothma's speech to the senate, which is why the imperials were scrambling to cut power to the senate chamber. Perrin and Sculden's wife both lost their spouses to the rebellion, which better explains them being together later.
There are videos and interviews on yt and the net, from the episode writer, and Gilroy, talking about it. Some were linked a couple of pages back in this thread.