Hi Jcat, our beloved Cat boy died May 18th of this year from complications due to feline leukemia (he had a tumor in his cerabellum). We first noticed him limping on April 3rd and he progressively got worse and was hospitalized numerous times during this period, mainly because of his continued refusal to eat. For over a month none of the vets could figure out what was wrong with him, other than a "guess" that it could be related to his leukemia status. So, during this period, I was on the internet every single night for at least 2 to 3 hours researching and reading every article I could get my hands on, desperately searching for information on what could be wrong with him...hoping we could find "something" and cure him. I can honestly tell you that I've probably read every article & research study out there on FeLV, sometimes twice, and never once read anything about a dilated pupil as an indicator for FeLeuk. Not saying you're wrong, but if it was a good indicator, it should have been mentioned in several of the studies I read and it wasn't.
I would still keep kitty quarantined until the test results are back as there are many other illnesses/diseases/parasites/fleas that can be passed on which you don't want.
Oh, and I should mention that Boy adopted us as a stray back in late 1999. We took him to the vet Feb 2000 for neutering & shots when it was clear that he had moved in, and that's when we found out he was FeLV positive. Thankfully, we were able to give him another 5 years of life where he was treated like the little king that he was. We miss him dearly.