Why is Ren such a gentleman? Because that kind of personality not only fits a 'party host', but it doesn't require many emotions. If he had to be emotional, he could fake it.
In Act 3, we learn candy people's memories and personalities are all stored in their eyes. The horror sets in during the flashbacks later on, to Halloween 2012. During Jackobel's rampage, we see several eyes lying about, colorful and maybe sugary goo leaking out of them. Jackobel didn't just murder people, he did what was roughly ripping out someone's brain and leaving it on the ground.
Prior to fusing with Jackobel, Ren pulls out a button which plays the song that summons Jackobel. He could have summoned Jackobel at any point in the party if he wanted to, and probably would have done it if Elias didn't force him to drop his facade.
