It is never a good practice to use the summaries as predecessors or successors (also do not assign resources, cost or work to summaries). Reasons:
Only a task/milestone/event can be a predecessor or successor
Summaries are just a way of organising tasks/milestones/events within the work breakdown structure
Just because the sofware allows it doesn't mean that you must do it
It is easy to create circular references.
Levelling won't work