Hydroponics = tasteless, if supermarket tomatoes are anything to go by.
I don't think it is the hydroponics that is causing the tastelessness of snoopermarket veg. I think it is the snoopermarkets demand bright red spotless bags of water that survive being shipped around the world and will last on thee shelves just long enough to make it into your kitchen.
I saw an interview a few years ago with a snoopermarket boss who said that they breed their veg to not have a strong flavour because it is more difficult for someone to dislike a subtle flavour than a strong flavour.
Have you noticed that you rarely meet anyone with garlic breath any more? That is because they are so weak in flavour that I have to put about 5 or 6 cloves in a dish to get any flavour.
So it is not how they are grown but how they are bred that determines the flavour and they are actively being bred to have less flavour.
This is one of the very reasons I like growing my own from heritage seeds that still have a full flavour
Back to the original question I think you will need to physically stop the slugs from entering your hydro set up as they will quite happily live in a hydro system. Even if you have a deep water culture system the slugs will find their way onto the rafts as soon as a leaf creates a bridge. A flood and drain system could be susceptible to slugs who will get in amongst the grow medium and an NFT system would be very vulnerable to slugs I would have thought.
Have you thought about breading your own nematodes that are specific to the slugs in you poly tunnel.
All you have to do is get a bucket with an inch of water in the bottom and a handful of weeds and then go around your poly tunnel at night collecting as many slugs as you can find. 20 to 30 should do. Put them in thee bucket and put a sheet of glass on top or a lid to stop them escaping. Give the bucket a stir once a day so the slugs are in contact with the water.
After 14 days all the slugs will be dead and you will have a concentrated mixture of nematodes (specific to your slugs) and slug killing bacteria. Strain out the solids and retain for the next batch. Fill the bucket up with water to dilute the mixture and use the water to water your affected beds. The treatment will last up to 6 month but probably longer in a tunnel where if will be less likely to be washed out of the soil.
Use the solids from the bucket to start of another batch. Add a few more slugs if you like.
Good luck
Paul