That's interesting because I found that Ulos means (of movement) out, outside; outdoors, in the Finnish language. Evans is said to have spoken a foreign language, I wonder what language it was.
I've wondered about that myself. I've searched the autobiography and only could find-
IMO it seems to be a mixture of truth and fiction, maybe even an explanation to authorities why he had a child with him. Maybe he knew he could be discovered soon and this was to throw them off so he wouldn't get linked back to Manchester. He might have not known Denise and Dawn weren't reported missing. The truths I think that are in the note was Lisa's mother being named Denise (we know that's definitely true) and that she possibly died in 1983. Even some of his upbringing may be true, like having 6 siblings.
To answer your question, it seems Ulos Jenson was spoken rather than written.
I found
another article that states that at one point he told people he was born in Wyoming as Ulos Jenson .
So it could be possible that the people he took misheard Ulos and that it could be spelled wrong.
My take on it is that I don't think he would tell people his real birth name on the run, and the last name Jenson likely came from his most previous alias
or was the alias he was using at the time. It also doesn't mention exactly when he told people, but it's most likely the late 80's before his arrest, so he either was using Gordon Jenson, or Gerry Mockerman at the time. Him telling people while using his Jenson alias would make the most sense IMO, people do change their first names in adulthood, it's not unusual.
IMO Ulos could be either a completely random name he choose or a vague link to his past, like his father, grandfather, or uncle being named Ulos.