There is not currently a syntax highlighting file for HL7, as HL7 is not intended to be edited by hand, as this would prove quite inefficient for the health care industry. HL7 Messages are intended to be be manipulated using the HL7 Tools.
If you are needing highlighting for HL7 because you wish to create a new HL7 tool for the health care industry, and you wish to make it easier to read the HL7 for better understanding so that you can write a parser for it, then that is the only way I can see it would make sense.
The only reason I know anything about this topic is because I was in the health care industry and health insurance industry for several years as a programmer for new medical technologies. I never wrote an interface tool for HL7, as it was introduced after I left the field, but I have a basic understanding of it.
If you need it to manually read/peruse/browse/edit HL7 messages in their raw form, then that is simply a bad idea. If you are trying to develop a new interface tool, then perhaps I can assist you by creating the HL7 syntax highlighting wordfile for you.
If you need an interface tool for HL7, there are a number that I could recommend, both commercial and open source. UltraEdit is simply not an interface tool for HL7. It would be like trying to edit Microsoft Word documents or PDF files directly with UltraEdit, which is not wise to do in a plain text editor.
Please let me know your needs regarding this matter.