I've come across many games running on 60hz motors and they seem to cope OK, it's just a bit irritating having them count slower! 50hz games reimported to the US go the opposite way and count 20% too fast, which can cause badly tuned games to struggle to keep up.
I first came across this a few years ago when I took my Jack in the Box to a show and it burnt the motor out. I was kindly given a replacement motor but when I fitted it the game seemed to play sluggishly. When I inspected the motor it turned out to be a 60hz one, so I swapped it out for a 50hz one and the game was back to its old snappy self
Your game may also have a 60hz transformer, possibly with an extra step down transformer to convert our 240v supply to 110v
The only issue I've read about is that the frequency difference does put extra strain on the components and can cause overheating and degradation, and may lead to premature failure, but How likely this is on the pinball components I can't tell you.
When I buy a game that has a 60hz. motor and transformer in it I usually swap them out for 50hz equivalents if I have them available, but if I couldn't find any I'd carry on using the game as is.
We could really do with a parts exchange programme with the US
A quick Google just now threw up this link
http://www.50hz60hz.com/60hz-motor-running-on-50hz-power-supply.html