We just met a really cool engineer but he doesn't have a work Visa. Anyone familiar with these situations and can provide some info?

Depends on what you're sponsoring. E.g., if you're sponsoring an EB1 visa (ext. ability green card) you may get a parole allowing him to work here until the petition is adjudicated (this is my current situation). For O1 and H1B I don’t think anything like that applies: also O1 standard are pretty high, for this year H1B lottery you're maybe late. Depending on nationality, he may be able to come here 6 months with a B1 as a contractor, i.e. paid by a company (possibly, even a company made by only him) in, say, Italy under a contract with your company. The crucial thing here is that the salary does not come in any form from the US. You can use then these 6 months to figure out how much you like him and next steps.