The only UV based white LED I have heard of was some prototypes that Nichia showed at a SAE convention a couple years back. Apparently you get less color shift with current change on a UV source but it has its drawbacks and safety concerns. The Seoul is a blue LED to my knowledge.
Most epoxies can have their HDT raised if you post cure them with an elevated temperature. The cautionary note on the heat of the epoxy may be based on structural and bonding considerations more than concern over the longevity of the material.
I used some really nice clear epoxy a few years back and posted about it but danged if I can recall the brand and I left the stuff back in CA so I can't look for it. It seemed to share a similar index of refraction with the epoxy used in the lamp style LED's and their envelope would disappear when cast in this resin. It also had some UV protection. Below is a pic of an Arc AAA I used this resin on. It was my first mod I shared on this forum.
This turned the Arc into a flood beam.