In 2015 edition of asme sec. viii div. 1, as per clause UW-11 a8 UT was permitted in lieu of RT under certain constraints.
But 2017 edition onwards, this clause has been removed.
I do not know if I am following your query properly. UT can still be used in lieu of RT per UW-51(a)(4). However UT has to be recordable like TOFD or PAUT. The below snapshot is from 2019 edition.