It depends. Clearing cache should only be done if there are specific instructions for a particular hot fix to clear any caches.
In the case of there being an update to a java class (as an example something in the Pega runtime engine) then a restart of all nodes is required because the java class loaded happens one time at startup.
In the case of there being only rules in a hot fix, then a restart should not be needed. The rule changes are propagated across the cluster and should be available on all nodes.
In the case of a mixed rules and java classes, you must also restart all nodes so that rules dependent on class updates are in sync with the loaded java classes.
Hope this helps.