This came up with a local dock builder.
Is UF allowed on a pier.?
There is some ambiguity in the NEC about wiring on piers. 555.13(A) says
(A) Wiring Methods.
(1) General. Wiring methods of Chapter 3 shall be permitted
where identified for use in wet locations
That would seem to allow type UF cable

but 555.15 (B) says
(B) Type of Equipment Grounding Conductor. The equipment
grounding conductor shall be an insulated copper conductor
with a continuous outer finish that is either green or
green with one or more yellow stripes.

UF has a bare grounding conductor.

The issue was direct buried UF coming from the house, then being sleeved in RNC out of the ground, up to the lift control box and other lighting and receptacle outlets.
I am leaning towards no. Transition to THWN before it gets to the pier with a compromise that this happen at the first J box on the pier.
I am not the AHJ here and so far none have brought it up but I am not sure how common the issue is. Most guys just run RNC and THWN the whole way

Up here it’s PVC/RNC with THWN, usually straight to the panel. Interior methods to get from a panel to a j-box is MC most of the time, to maintain an insulated green ground conductor. I say ‘most’ because I hear that NMC is installed in some towns.

The debate for the NMC inside is that it is approved, as the location is dry, and the change over to THWN in a j-box inside the structure is compliant.

Why would someone volunteer to pay for the extra cost of UF cable rather than just using THHN?
You've got to run it in a raceway on the dock anyway to protect it from physical damage...and UF is a real bear to pull through conduit.

I guess if they have that kind of money to throw around I would caution them about some UL cable not being UV resistant since at some point the conduit protection will likely end.

I believe they were thinking that they could just use UF all the way and avoid conduit completely.. I shot down that idea right away. I agree with you, why would anyone want to use a cable if there is conduit involved? Maybe it is because of the up charge home stores charge for cut pieces of THHN/THWN when they are buying cable by the roll.
Guys working 1&2 family do not use that much conduit around here unless they are wiring pools and that tends to be a specialty contractor. Maybe that is the guy the dock builders should be using anyway. The requirements are closer to being the same.
A wise customer would spec conduit for buried work anyway, for the extra protection and for the possibility of upgrades without digging in the future. I am just not sure most customers are that wise. They only look at price, not what they are getting for the money.