Custom nodes required to run DYN files?

Does a DYN file run if a user hasn’t installed custom packages/nodes?

It will run… but your results may not be as expected, and likely flat out wrong in many cases, if the user doesn’t have access to the packages which contain the custom nodes that are used in the graph. Best to annotate the custom nodes in question (or make use of the dependency manager in recent versions) so you know which packages any given node came from. Monocle can help with the annotations.