Really smart gamblers would find out the algorithm used by the betting companies to flag unusual betting activity. And then do their betting so that they fall just outside of its parameters. Or if you can't be bothered being that diligent, just blow some of your winnings by putting a lot of money on rounds where you don't know the results.
But this does give me a good idea. If there is a WC loving ump, then form a syndicate and bet heavily on all WC games that they officiate in. Just enough so that both the ump and WC come under suspicion.