Wikipedia defines polymath as person whose expertise spans a significant number of different subject areas; such a person is known to draw on complex bodies of knowledge to solve specific problems
But if you want to put it in simpler English, I would call it a person who has a basic understanding on a lot of different things.
Now add "Marketer" to the mix and it gives you a person whose marketing knowledge starts with a basic core knowledge of a significant number of marketing techniques and an expertise in a some. Thus giving him the ability meld several forms of marketing to find the best fit for each customer's marketing needs.