Ya, i guess i see his point, but this isn't something that would be a detriment to the system. Its like saying well technically you running a MH is taking water out of your system (evaporation) so it is bad for your tank. Well... no its not. Yes he's right, a skimmer takes out a ton of things, and I can't remember the poster (very intelligent guy) but he listed the 25 or so things a skimmer does take out. It takes out food particles, as well as minerals in the system (all-be-it very little). Definately run a skimmer, and if you want run a UV. The two issues i've read with UV's is that they cost a lot and add very little benefit. They add benefit, but not a ton (fuge, skimmer, hob filter all provide way more positives to the home aquarium than a UV). The second issue is they don't discriminate upon what they kill. Yes they kill bacteria - but this is good and bad. They kill pods, beneficial bacertia, etc. But at the same time they are killing ick causing parasites, as well as a ton of others (good and bad).
No, they will not work against eachother, and the plants you are adding to the fug not only take in some nutrients (and nitrates) from the water for their food source, they also will use light as a food source. My vote would be just to run a fuge and leave it be. You can run a UV if you have creaters like Tangs that do their best to find ick.
I hope this helps, and its your tank, i mean do what you want and what you feel best fits your situation/budget/and what you want.