What multicast guarantees does passive replication provide?

Have you got this the wrong way around?

With active replication you have multicast and if you need the order to be the same on all nodes you have a problem to solve. ie atomic multicast

With passive replication the primary node does the processing in order and then sets the state on the other nodes. So it's an easy(er) problem to solve.

ie you don't have

1. set x = 1
2. set x = x + 1
3. set x = x * 2

processed on every node and having to ensure that they are processed in the same order to have the same x at the end. You have the primary node running those commands and sending:

1. set x = 1
2. set x = 2
3. set x = 4

to the other nodes.