As far as I know, the bands will play whatever they like. There's no "soft" format, so I would imagine Opeth will play whatever their big hearts desire. Ditto to Katatonia.
Paatos won't be playing as Stefan will have enough on his plate without having to deal with playing as well!!! On the last boat trip, he was running around like a mad thing, with no sleep as he was doing too much as well as playing (Morte Macabre). So this time, I think he just wants to be there for the bands, etc. And have a chance to hang out as well!!!