Design is way way more than logo and paint. Interaction design is just plain being able to make stuff that works well for people -- that's the kind of design I'm talking about. Should have made that more clear.
As you say, design is a lot more than some paint and a logo. Interaction design, information architecture... are all VERY important at the early stages. I do think the early devs should have this as a skillset though (much as you do) opposed to cofounding with a straight up interaction designer (no matter how good they are).
Given the amount of equity a cofounder gets it I would tend to look for people who could be 100% utilized (working all the time to get the company up and running). It can be hard to keep a full time designer busy unless you have a team of devs pumping stuff out for them to craft.
As a side note, I've seen early design hires hold back the company in later stages as they tend to wield too much power over the product (often playing a pseudo product management role).
It's easy enough to outsource a logo and some paint. Think about your use cases and make sure the service caters to them but good product is often "designed" at the functional level.