Hi

yes it is possible using Mic input with an MC cartridge which has low impedance. Needs correct cabling to Mic Input though.
RIAA can be done by an RIAA equalizer  after the amplification of UCX II. For example with a FIR-convolver (acourateconvolver or other) which implements RIAA.
You have to try if the noise level is okay, means better than a good RIAA phono preamp.

Or offline recording with audacity or Vinylstudio (both contain RIAA EQ)

Thanks for all the feedback. I thought there would be a reason I hadn't seen it as a solution before.

Sounds like a very expensive experiment hooking up a mc pickup to digital interface just to apply a digital riaa conversion. Better connect the riaa preamp to ucxII, work out gain issues, apply some EQ and maybe some expander.
Im not an engineer, but I dare to say that riaa filtering is the easier part of a phono preamp, amplifying the small signal is the harder.

I get lousy gain from my riaa(Cambridge audio CP1 MM). Waiting for some cabling to test it out with UCX. Need at least 10 more db to get the same level as digital. Moreover some of my records could do with more or less bass, some analyzing and adjusting here.

Digitizing LP's is probably fun, but kinda think it defeats the purpose of the sweet laid back analog sound. I dont know, but ive heard some really shitty digitized records. Noisy and totally lifeless sound. While better attempts can be "listenable". Seems to me that the digitizing mostly bring out the lesser sides of analog recordings. They where mixed to fill a dynamic range of 70db. How can U fill up the rest of the DR of digital?