I spread ash in my yard, it's been fine. We can use anything to increase top soil depth here in VA, especially on this side of the mountains (and the neighbors kinda got mad when I spread chicken litter the first time). If you have a pH issue with the ashes then add a bit of ammonia. Not only will it bump the pH up for you but will give you a nice N addition.
Brinkman Sportsman's Smoker, Gasser, Weber Performer, UDS