I asked around about this at Advoco but unfortunately we're not sure what the current limit is. I advise that you go to Infor support with this question, they should be able to answer it. That being said, the database limit for columns is 1,000 so the max won't be higher than that.
Now, there's something I feel that I should mention: Needing that many fields on a UDS is sometimes a red flag for poor functionality design. I don't know the context for this question so you may have a perfectly valid use case for this large of a table, but I just wanted to at least make you aware of how extreme this scenario is.
Let me know if you have any further questions about this.