Most wild yeast struggle to ferment wort, but there's always the chance of getting one of the ones Nosy mentions.
Dump or not is really your call, and heavily influenced by the need for the beer, as much as the risk of infection. If you don't NEED it, you're weighing up the cost of the yeast vs the cost of dumping. With many of my beers, the yeast costs less than the hops so I'd just start up another starter. But your costs will be different.