He should have some idea
That's a good question you have.
First off, what does he do in the military?
As to symptoms, there are some that seem to show up over time, from what I have learned in corresponding with and speaking with some of the Gulf War vets.
The first thing I would expect him to notice is an overwhelming fatigue. You can ask him about this. ... and a change in personality - 'fly-off the handle all the time over nothing!' (You'll notice this yourself)
One gulf war vet shared that her group only cleaned the equipment on USA soil when it was returned from Saudi - using Dawn for 10 days continuously (& with no protective gear) - and that the whole group got sick. (another vet shared the same; so it is not an isolated case; plus it is listed as a group who came down with symptoms - the chemical of concern in that case is the simplest form of ethanol. But it's the exposure, I guess. Too much exposure to even this simple form of 2-butoxyethanol type of chemical ... & the same harm?)
In her case her doctor found that she had too many immature red blood cells. This is what I would have expected from too much exposure to 2-butoxyethanol or diethylene glycol monobutyl ether ... but not from the ethyl alcohol.
So, have him ask the doc to do a 'retic ratio' and to have the lab tech look at the red blood cells (What size are they? What shape?) Also check for iron storage and utilization; plus kidney and liver function. Ask him about headaches that are really odd. So for preliminaries, I think this would help. Remember after all these years, there are many theories, but no for sures ... with all that has been studied; (this chemical I'm talking about has not been studied regarding the vets, that is.)
I believe this is the chemical of harm (2-butoxyethanol family of chemicals) based on it being one of the chemicals listed for gulf war vet exposures and based on it being the only chemical of harm of the Exxon Valdez oil spill cleanup. AND the symptoms there being 'gulf war syndrome' type symptoms.
Now, there have been some Exxon Valdez oil spill cleanup workers I've talked to who have not been able to have children. One was a 'biorememdiation' worker I spoke to last night. He hasn't seen a doctor in 8 years; he didn't think about being ill from this job. Another is a US Coast Guard monitor of the biorememdiation experiment. He told me that his endocrinologist is stumped by his having zero sperm.
According to the info on 2-butoxyethanol it targets the testes and can cause reproductive harm. There is another biorememdiation worker who had more exposure than the first one I reference here ... and he has 3 very healthy happy children whom he and his wife adore.
Let's pray your loved one will not be overly exposed to any harmful chemicals and that you will have a long life and healthy children, too!