Can you ask a Protestant to pray for you? Of course!
But why would you want one to when you can have a priest or religious do so for you, which will be more efficacious.
Whoah! We have to be very careful here.
Priests and religious do not have anymore of a hot line to God than any other person of faith.
The Catholic Church believes that prayer is prayer, regardless of who does the praying.
I would ask as many people as I could to pray for me. God does not have a preference for the prayers of Catholics.
Br. JR, OSF