I imagine you already tried this, but when I plugged the words cornmeal and soap into Google, > 6000 Web hits popped up, and about 600 on the newsgroups. This site says that Maine Organic farmers were the inspiration for their rosemary and cornmeal soap:
Not all of the hits are for cornmeal in soap, but some soapers are using it. Maybe the soapers like the Maine one above can tell you what they have up their sleeves.
I don't know whether most of the soapers are using cornmeal for antifungal or other properties or for abrasiveness/texture (in solid soaps). I imagine the situation may be limited to cold-process, as I wonder if the antifungal character would survive hot-processing -- I could be wrong about that, though. Other than temp (and maybe processing pH), my other concern would be shelf life on liquid products. It might be tricky to preserve the antifungal properties without causing microbial blooms, but that isn't to say it's impossible. That may explain in part the reason that the people above add rosemary, but then they seem to be dealing with solid soap. I also wonder if the sap ingredients can be adjusted to retain the cornmeal character as much as possible. How, I don't know -- maybe using KOH instead of NaOH?
Where in the manufacturing process do you envision adding the cornmeal/cornmeal juice in either solid or liquid products? I wonder if any of the constituents of corn react in the sap reaction or react with any of the typical soap ingredients. Corn pH runs about 6.5, but adding cornmeal to the heart of the sap reaction would seem to me to be a way to make something close to hominy. If you're thinking about the antifungal effect of cornmeal, I suppose one way to test it is to compare your own plain soap vs. plain soap with cornmeal vs cornmeal juice vs water on a fungal sample (maybe a shower grout black fungus?). If you're thinking about other effects from cornmeal (which one(s)?), that might be a more subjective test. Maybe we can brainstorm about this some.