There is a lot of debate on that in the orchid community.
The argument against it is that the plants cannot take up urea directly, so it needs to be converted into nitrate and/or ammoniacal nitrogen first, and that the microorganisms that do that efficiently live in soil - something we do not grow orchids in.
On the other hand, doesn't urea dissociate in solution?
all I can say is I once killed a cowhorn orchid that a friend brought back from Belize for me with urea and it was almost instant it turned black over night after f years of babying it and it just starting to actually get bigger every ne growth.....
It was most likly my fault and too strong but still .....
For what it is worth, I have used a urea based fertilizer for years in California, with excellent results for orchids planted in both fir bark and CHC/coir mixes. Weakly/weekly.
I am experimenting now with the MSU fertilizer on a portion of my plants, but the control group is still on the urea based. I will let you know next year what I find.
Virtually the entire orchid world used urea based fertilizers with great results prior to the introduction of more erudite formulas. Just follow the instructions on the container (it should be one recommended for orchids) and use as mentioned earlier. Regular weak solutions applied each week tend to work the best with any formula, urea base or not.