It's wonderful to have both options - let that be said first. The Lexicon 480 offers a dated but still compelling and undeniably classic palette of sounds and it's amazing to have basically the same sounds ITB, especially over many instances and at a much lower price.
I sold off my UA DSP cards a few years back so can't compare these directly. That said, I did listen to examples of the UA model and feel very familiar with the Hw and Relab sound. I don't think the UA product has any sonic advantages over Relab's. Realistically they are probably both complete substitutes for the HW, minus the tactile LARC user experience.
For anyone comparing UA and Relab keep in mind that parameter values aren't going to be 1:1. I know in some cases Relabs ranges were expanded or parameter scaling was not 1:1 with the HW.
Small differences in shape/spread, reflection levels or the filtering make substantial differences in the overall envelope and how the tail blends with the source.
Also Relab has options for 18 bit truncation, saturation, and three selectable outputs - digital, analog and analog aux (both with and wothout noise). These absolutely make a sonic difference and give it some exta character and melting/blending magic.
If you're comparing Relab with the HW be sure to use the analog with noise outputs (assuming your 480 is running analog).
Relab has the super dense R Hall HD, extra chorusing modulation, split and cascaded routings, and is very low CPU. Any missing effect banks may be included with a later update.
BTW - For anyone who hasn't tried the non-standard machine routings (like A into B or A for L B for R) you're missing out on some really fun sounds. A stereo delay or pitter patter type setting feeding a hall or plate sounds awesome. I often use a simple echo from machine A into HD RHall on B doing a really small, short but dense ambience. Awesome thick diffused delay potential.