Here's a good read on the effects of an oil slick on a hurricane, but note the illustrated extent of oil-covered waters:
Wunder Blog : Weather Underground
For areas upwind of the oil slick, I'd say it's plausible that you're seeing hotter, drier weather because of it.
I would describe Buffalo's summer so far as "cool and wet, punctuated by a few heat waves". It's 75°F and rainy here, and it looks like I won't need to put the A/C back in the window this week or next.