I use distilled water in wine making. Is campden necessary when I use distilled water?
Campden (or rather sodium meta-bisulphite, which is its active ingredient) serves multiple purposes in wine making. It removes chloramine from municipal tap water, but in your case that is unnecessary since you use chlorine-free water.
It serves as a microbial inactivator, which means that in low acidity musts (i.e. insufficient acidity to keep microbes in check) it helps to prevent microbial infections.
It serves as an oxygen scavenger, which means it acts as a wine stabilizer that prevents oxidation. In commercial wine making it is commonly used for this purpose, the 'Contains sulphites' notice on the back of bottle refers to sodium or potassium metabisulphite, i.e. Campden.
So even if you don't need Campden to de-chlorinate your water, it can still be useful in wine making for other purposes.
If you are using distilled/de-ionised/RO water for beer brewing or wine making then Campden tablets are not needed to knock out Cloride ions from the water as they are not there but, you may still want to use a small does of campden in wine making to inhibit wild yeasts and bacteria, if you are using raw fruit.
And... yes there is more ...
You will if using RO/Deionised or distilled water need to add back salts to the water to give your yeast sufficient magnesium and zinc or other trace ions that yeast require for a healthy fermentation, and to get the correct mouthfeel for what ever you are making.
Where I brew I know my water is low in magnesium, so I treat the liquor with epsom salts, as there is also low sulphate. I used campden to knock out chloride as the cholramine used by the water board is difficult to get rid of otherwise and can lead to medicinal flavours in final wine/beer. I also due to the high carbonate levels treat with a little lactic acid, to reduce the pH so I can reliably hit optimal mash pH; which is less of an issue in wine making.
You may want to take your water to a state of containing some ions or your mouthfeel will likely feel weak and underwhelming, and the yeast will end up stressed due to lack of trace nutrients in the form of dissolved salts.