Seeing as the grommet is exposed to the brew underneath during a normal fermentation, I would not sweat it too much. The only thing I might be worried about would be off flavors from the rubber, like water from a garden hose, but it is a microscopic amount of material relative to the amount of brew, so I don't think that is an issue, and since it was sanitized, I would not worry. Just remember to get it out of the trub when you rack, or next time you won't have a spare
RDWHAHB!