Hi Tony ... good to see a new member posting!
Passionfruit would be too tough for the fruit fly.
Getting the soil right - the microbes, the organic matter and with regular watering and growing crops in their season, there should be little problems with fruit fly. Or other pests or diseases.
Hi Tony, in my experience fruit fly mainly attack my tomatoes, capsicums, chilies and fruits like guavas, feijoa. I don't think I have seen any problems with cucumbers. No problems with passionfruit. Good luck with your exclusion bags. They have been a help to me.