My guess, based on crude extrapolations from reported nutrients of other dried foods, is that you'll get half the nutrients of fresh mussels.
That ought to be a clear improvement on a vegan diet.
I suspect your main remaining reason for concern might be creatine.
My guesses about why vitamin pills tend to be ineffective (none of which apply to dried mussels):
* pills lack some important nutrients - ones which have not yet been recognized as important
* pills provide unnatural ratios of nutrients
* pills often provide some vitamins in a synthetic form, which not everyone converts to the biologically active form
My nutritionist said freeze dried plant powders were worse than fresh picked produce but equal to or better than anything else ("freeze dried" is loadbearing there- heated powders are worse). That may not translate directly to animals but seems like they will definitely retain something.
Personal background for this question:
Oysters and mussels seem like they might have important nutrients that one otherwise can't get in a vegan diet without supplementation, just because that animals are different to plants/fungi/etc., and humans ate animals in the EEA. However, due to their disgustingness, I can't quite bring myself to eat them.
Luckily, it turns out that one can buy capsules that contain freeze-dried green-lipped mussel powder. I'm pretty excited about this prospect, but am somewhat worried that the freeze-drying and powderifying process would destroy various nutrients, or render them mysteriously ineffective in the ways that I gather vitamin pills are mysteriously less effective than vitamins in food. I also imagine that maybe the really important nutrients are only found in (say) land mammals. Can anybody shed light on this?