Seaweed is a good source of iodine, but also has a lot of bromine which can affect your absorption of other minerals. No reason not to eat it, but balance is always the key!
I'd also be concerned about how salty nori is - but really, you just need to make sure you're drinking heaps of water with it as well (will help with weight loss anyway) and you should be OK. I'd reckon on 200mL (small glass) with every roll.

Itadakimasu!