Ask HN: Need advice on raising money with a part-time founder.

Myself and my co-founder originally started our company on the dream of being apart of the solution to healthcare. Being a front-end/back-end combo, we had little "healthcare" experience, but we thought that we could make it work. We realized we would eventually need to bring on someone with healthcare experience. We did this about a year into the company when we brought on a very well known figure in the Health IT world as a part-time "co-founder". Among other roles, he is a practicing physician. At the time, although he was not working full-time, we decided to give him founder equity in the company. Everything would be split three ways - 33%. We viewed his part-time efforts as being acceptable because he was in the field, figuring out the problems in healthcare... Since then everything has been going well. Myself and my original co-founder are working full-time on the company, we pushed out a successful beta, have a paying enterprise customer, etc. The doctor co-founder has been proving his worth - he is actively involved in the product, helped us sell to our first enterprise customer (gave the presentation), has been tracking down new leads, and has been talking with potential investors. That said, some of the investors we have been talking with are seriously hung up on the fact that we have three founders and only two of them are working full-time, going as far as saying that this would turn many off from investing. The way we see it, he has been crucial to our success thus far even though he is only working part-time. He provides a role that we could never do (be a doctor). Will our cap table, as it currently stands, cause us to be unable to get investment? If so, what is an acceptable level of equity compensation for someone in this role?