The answer to both questions is – it depends. Generally, it is best to have one server manage the replication (IMHO) but some prefer both servers do it, each doing a push only replication.
To me, in a cluster situation, generally one server is there only for failover anyway and is not likely doing too much. So having it do a pull/push replication (thus using its resources for the activity) is best and not having the production server do anything.
The key, I guess, is that the server the initiates the replication does the work. So if, in either configuration, you have one server with a smaller load, it is likely best to have it do all of the replication.
I should mention that clustered boxes do not have to use the cluster replicators. So if they are connected via a WAN for some reason, just use regular replication on a short schedule instead – it is more efficient. Cluster replicators are very active. It is also possible to have just some databases use cluster replication and others use normal replication. It is actually recommended you have a regular replication connection configured for clustered boxes for the specific issue that a database may not have cluster replication on, so it will still replicate. Also, the cluster replicator queues activity and is not always immediate anyway – so regular replication fills the gap.
I could write on this subject for hours, if you need more info contact me through my contact info on my website (www.acadiasolutions.com). I am available to assist with Domino admin tasks as well.