I guess that depends on how you value parts, and how you value originality in a pistol.
If you are selling parts, it is hard to say. There are far fewer people needing a good UMC barrel. So, even though they are rarer, that doesn't mean the demand is any greater.
The Colt barrel, however, is probably in higher demand because so many more people have Colt pistols that may need a barrel. Who knows? It all depends on who needs what and what you have, along with its condition and whether or not the barrel is authentic and original finish.
Now...if you are asking about the value and desirability of your pistol...that's easy. I'd always rather have an all-original piece with nice condition. If no condition, then at least original.
BTW, nearly forgot to answer your first question. Yes, it might be a UMC barrel. But, it may not. Photos will help determine what it is or might be.