Why not both?
Putting the Royal Engineers in tier 1 makes a lot of sense for early game CQB but are still fairly weak compared to dedicated CQB units like Sturm Pioneers and Assault Engineers.
But if you put them in Tier 1, AND give them a Hammer Tech upgrade then UKF build orders might include Royal Engineers more often in the early game but also promote keeping them around late game regardless of whether you go Anvil or Hammer.
I don’t know about the UC though. I like the proposed unit design but without it in tier 1 UKF lacks a sniper counter until they tech up.
If you also reworked the Infantry Section’s recon upgrade to include a pay per shot snipe ability, passive cloak and a single scoped Lee-Enfield, a No.4 Mk1(T), then Infantry Sections could be used to counter snipe a sniper, but not be economical to be using the ability too often. It would also have to take up at least one, maybe both, weapon slots so you wouldn’t want to spam them and be able to “double tap” or “triple tap” a Grenadier Squad for cheesy wipes.
I think it would work, and was already done in CoH 1, so the idea is sound, it would just require adjusting the costs around a bit to make it balanced.
My point of putting royal engineer in T1 is to support, as said, they provide early capping power, close dps protection for sections/vicker mgs, to avoid easy rush, and flanking if opportunities appear, but they are still not dedicated cqb unit. Royal engineer as now already have decent dps (comparable with pioneer) and 0.9 target size, i think this is enough to be very effective if combined with sections in early game. Dont get me wrong, i definitely like Thompson smg but latest tech is too late, i suggest a side tech in T2, as Thompson and satchel will be more useful in early mid to mid game.
About your concern about counter sniper if UC is moved to T2, i think it will not a serious problem. As now, using UC for sinper hunting is not very effective, since UC is not fast, fragile and snare is everywhere. Meanwhile, UKF's sniper just got buff so counter snipe with him is easier and sure is a better choice, and you have more field present with RE in T1.
I believe RE in T1 will improve UKF early game, while Turning UC into a truly fighting LV in T2 will bring more diversity to UKF mid game/lv play.