I think a mil is high. That article is likely to be true, but misleading. You know how in ball sports, the amount the teams pay players is not a mystery....yet, people always say stuff like 'oh, if you count what LeBron gets from Nike....'
They consider the widely known figures from football or basketball team to be the main thing and product endorsement as sort of a sideline even though it's probably just as big a number if you're in LeBron's visibility category. In running, product endorsement is considered the main income by the fans. So the number around 350 may be what he does, in fact get from Nike - as a base. He's going to have bonuses for medals and records.
But all that doesn't include money actually generated by racing, which is a combination of prize money and appearance fees. So that can be as much as your shoe/apparel contract, or at least the base salary (assuming the number mentioned is close to accurate) if you're on top of the heap. So if you count everything - and of course you have to because it can all be spent - It is certainly more than 350k, and probabaly close to a mil, but that much seems (just a little) high.
I'd say $800k. That is, of course, just a guess.