Create a single field address locator based on the mile marker feature class with the mile marker identifier as the keyfield. As long as your crash data has the same format/value for the mile marker as your feature class identifier field you should be good to go.
Once you geocode them, they will 'stack' upon each other since you are using a single point to match them to. You can do your stats with a summary table based on the mile marker identifier; you'll get a count of all the crashes at mm 1, mm 2, mm 3, etc. Join that summary table back into your geocoded points and you can display then by the count ( 47 crashes at mm1, 3 crashes at mm 2 etc).