UTV used ITV-branded trailers provided by the ITV company who produced the programme (e.g. Granada-produced programmes with the Quay Street announcers on voiceover and the text using whichever font Granada used in its general presentation package at the time) up until the June 1993 Year Zero relaunch; one or two ITV-branded trails still slipped through the net, or trails rebranded with the UTV logo sometimes still had the voiceover of the networked trail with references to ITV either kept it or muted out, but by early 1994 at the least, Havelock House were wholly producing their own versions of networked trailers..
Many of the ITV regions appear to have begun producing locally-branded versions of network trails in early 1993; the network trailers of the time featured an ITV logo in a black lozenge; I remember UTV replacing it with the blue/yellow oscilloscope logo (for the last few months of its life), and I recalling seeing off-air screen captures on pres sites with Border and Tyne Tees local adaptations of this trail style template.
Regarding interesting YouTube videos, from 00.20 to 00.30 on
this report about ITV Telethon '88 (channel: terminus69), monitors in a gallery at The London Studios (most likely Studio 1) are shown with a set-up of nine different feeds taking content from various parts of the ITV network:
To clarify what is being shown on each feed:

The first is the Granada feed, carrying the output from Border and Scottish (with Ulster's content travelling via Border's link and Grampian's content via STV's link).

The second is the ITN feed, carrying the output from TSW, HTV West and Anglia (with HTV Wales' content travelling via HTV West's link)

The third is the Central feed from Birmingham, carrying the output from Yorkshire, and Central in Nottingham (with Tyne Tees' content travelling via YTV's link)

The fourth is the TVS feed from Southampton, which is carrying the output from TVS in Maidstone.

The fifth is the Thames feed

The sixth is labelled (L?) Studios and Channel TV (surprised to see them having their own feed rather than travelling via TVS!)

The seventh is labelled Riverside Camera, a feed to an exterior shot of the South Bank where an "egg-crate" roller box gave updates on the Telethon total

The eighth, I can't make out what the label reads

The ninth is labelled LWT OB (say no more)