I'd be a little concerned about the screen restricting airflow, particularly if you're in a hot climate.
Most gensets move a lot of air through the cabinet for cooling, so a close woven screen could be restrictive.
I placed the screens on the genset about 5 years ago. Summer temps can get over 100F but usually in the 90s at my location. To date no issues.
A year or so ago the unit ran for about 2 days during a summer outage with high 90F temps. I don't believe the screens have had an adverse effect,
but your point on airflow is well taken.
As for UPS's note of dirt build up on screening since they are attached with magnets they are easily removed and hosed off. I do this to mine end of Spring and
Summer. A couple of minutes to hose off twice a year is an easy thing to do and better than finding out the inside of the cabinet has a wasp, hornet, or mud bee
colony, all of which are numerous at my area.