Hey - no and no - you can either establish a Puerto Rico only plan or a Dual Qualified plan. Most plan sponsors create a separate plan for Puerto Rico employees because the difference in limits, rules, etc and usually is simpler to correct any involuntary mistakes by the plan. As CuseFan said, it is important to take into consideration how many PR employees the plan sponsor will have vs. the ones US based and the benefits provided to them.
We are a local Puerto Rico TPA firm (Pension Plus, Inc.) in case we can be of any assistance to you.