Especially in a small company, the founders are going to have a few "small pebbles" that can get stuck in the machinery. If you try to ignore/override the grinding noises, you're engine is going to blow up. As painful as it might feel now, I think your best option would be to back off and let Tom do whatever he feels is important (like the website).

The key is: DON'T make him feel like you're ignoring him or don't value his contribution (even if you don't). Just give him some time to cool off and don't pester him.

From your perspective, you might loose a couple of weeks, but at least you won't loose a valuable team member.

Database people can be especially finicky in this way (I would know, I'm a database person :) ). As far as I can tell, he just wants to feel like the company is also striving for the objectives he values. Let him work on those objectives for as long as he wants, but I'm relatively sure it won't be more than two or three weeks. He'll finish whatever is bothering him, and he'll want to get "more involved" again, which is when you start asking him with database help on your other projects.