Person A wants to redeem BA Avios. Person A has no BA points but has plenty of Amex membership rewards convertible to BA.

Person B has plenty of BA Avios.

If person A wanted to avoid the delay of converting BA Avios and instead had person B redeem award and then converted Amex rewards into the BA account of person B.

Technically I would think that this is a trade of BA for Amex or even other BA and a violation of the rules. Practically I would say enforcement to this level is rather harsh.

I guess more basically is borrowing miles to be paid back with identical miles a violation?