Yes. The latest poison effect will take place.
So let's say you had won the first round with Dolly in Fight Club. Your opponent will have 10 life. Round 2, you win with Ghelisting. 3 damage + 2 poison, your opponent will have 5 life. From round 3 onwards, your opponent will drop 1 life each round.
This is probably the reason why Wurmhol isn't really that popular. He does not compliment Dolly, a staple Gheist card, at all.
I'm not 100% sure I'm correct, but I'm 99% positive and pretty pretty sure that's how it works.
The posion with the highest minimum works first but as soon as the minimum is hit the other posion takes effect intill its minimum works. That means if you use gork to stop Karrion as soon as the minimum 4 is hit karrions posion starts again.