If there was any doubt before, it's now official. It has been a custom for years for marrying couples to ask a friend to perform the ceremony for them. I myself performed a number of marriages by becoming a "special judge" for the day. I think the most common method though has been for the officiant to become a Universal Life Minister, or to be "ordained" by a similar entity.
For years, the Tennessee statute on marriage has said that marriages may be performed by "all regular ministers, preachers, pastors, priests, rabbis and other spiritual leaders of every religious belief, more than 18 years of age, having the care of souls…" and "(2) in order to solemnize the rite of matrimony, any such minister, preacher, pastor, priest, rabbi or other spiritual leader must be ordained or otherwise designated in conformity with the customs of a church, temple or other religious group or organization; and such customs must provide for such ordination or designation by a considered, deliberate, and responsible act."
An opinion from the Tennessee Attorney General theorized that someone who becomes a minister online cannot be doing so by a "considered deliberate and responsible act", thereby throwing the legitimacy of online officiants into question However, until recently this wasn't an issue; county clerks did not question the authority of the person signing the marriage license and presumably the only time this issue might come up would be in a divorce proceeding (i.e. where one party would argue that there was no valid marriage).
The new amendment to the law adds a section stating that "persons receiving online ordination may not solemnize the right of matrimony". The question appears to be settled although I have read that groups are attacking the new law and it will probably end up in court at some point.
The biggest issue that people were concerned about was the question of whether their own marriages performed by a Universal Life Minister were valid. The law gives some certainty in this area by stating that "if a marriage has been entered into by license issued pursuant to this chapter in whichanyminister officiated before July 1, 2019, the marriage must not be invalid because the requirements…have not been met". This should cause some relief to those people wondering if they were legally married.