They can't really be particularly syncronised in the first place, since they're tracking entirely different things. Glacial Hammer is tracking successive strikes with the skill, and a given skill use will make one or more strikes (depending on when it repeats). And they have to be directly successive, doing anything else "breaks the streak".
If you never repeat with glacial hammer, so each skill use does a single strike, then Ruthless is still going to be every third use, while glacial hammer's bonus is applied if you use the skill (and thus strike) three times in a row without doing anything else, so they'll be doing different things if you ever use the skill a number of succesive times that's not a multiple of 3.