I think athletes have a lot of sway in society. I would definitely want a professional athlete as a partner for an investment. They have a lot of funds to invest and can help promote the investment. I think with a smart business partner, the investment could be very successful.
I would because that would be a nice way of advertising my venture . With the right people and the right strategies a venture can become very successful. It is just a matter of who you can find and splitting the stakes properly. Companies do it often so why not.
Why would I want to? They don't know anything about investing. They know about playing games, and that's really it. I'd much rather partner with someone who knows what they are doing, and will help me to make money. There's no reason I'd want to partner with an athlete at this time.
There's a great 30 for 30 documentary called "Broke," which details the crazy spending habits of professional athletes and why so many of them blow their salaries. One thing that struck me was their propensity for investing in clubs and restaurants -- typically terrible investments, but purchased because they enjoy them, and the thought of owning a club is more appealing than practical. This isn't to say an athlete can't have a great business sense (Fran Tarkenton sure had the tech industry pegged correctly) but statistically, I'll pass on investing with an athlete.