How does pineapple affect umami when used in vegan-fish-sauce recipes?
Umami is the result of glutamic acid (ions) getting in touch with the tongue. Glutamic acid in fish sauce is the result of a fermentation process, which involves bacteria doing the work of breaking down fish components. Glutamic acid easily dissolves in water though. This is after all, how it was detected millennia ago and centuries ago verified by creating glutamic acid salts: Cooking seaweed in water and boiling the result down.

The wakame is added due to its natural content of glutamic acid. There isn't anything special the pineapple can/has do to it that regular water can't do.

Therefore the answer is: No, the purpose of the pineapple is not to increase the glutamic acid of the substitute.