In my humble opinion;
This question is really quite 'Buddha-centric'.
Kind of like the Christian-centric and Islamic-centric dogma that ONLY believers can get to heaven (or hell for that matter!).Layman Arahant.
Do we only permit 'Buddhists' to be Arahants?
Is there a guidebook/manual with all the specifics and exclusions........
I am certain there are many people, like me, who (looking back) discern the shadow of the Arahant in their Mothers. My Mum's life of selflessness and unconditional love have been the main motivating factors in my practice. And she, a semi-literate Maori, never read a book on Buddhism.
Seems we 'Buddhists' can be as exclusionary as the jews, Christians, Muslims etc etc.
I guess Mother Theresa, Ghandi, Te Whiti o Rongomai (pre-Ghandian passive resistance in New Zealand 19th century) are all on the outer until they've read the Pali Canon and been to a dozen vipassana retreats?
Metta, karuna, muditta, upekha.