since I am allergic to shrimp do you think finely chopped salmon would work?

I would not finely chop the salmon as you run the risk of overcooking it.

http://food52.com/recipes/17048_vegetarian_okonomiyaki_with_homemade_chuno_sauce
just search for okonomiyaki in recipes above, and you can find variations. It's like 'pasta', how many variations do you know for pasta?

salmon would work fine mixed in with your batter. If using pork, cook it first, because it's pork. As usaba dashi says bonito is traditional, usually generously sprinkled on top. Or try my other variations: finehttp://food52.com/recipes/17260_beef_or_prosciutto_ham_chive_okonomiyaki_with_homemade_chuno_sauce

Buy Bonito flakes (ingredient for dashi). They are more traditional for okonomiyaki. Bonito is a dried fish flake of the tuna family.

I am sure it would, I have read comments where others used chicken, pork, just vegetables so I am certain that salmon would be wonderful. This is such a fantastic recipe I know you will enjoy.