Is energized protodermis the only method of creating Rahkshi or are there any other alternative methods?
No, EP is the only substance that can transform kraata in that way.
A follow-up: can Rahkshi armour be constructed by Makuta? Teridax did, after all, create Kraata-Kal’s armour.
Not to mention the 2010 Rahkshi armor which was modified to be more resistant to Takanuva.