Ok if I understand your correctly you mean say the FSB is 240 and the ram is 240 would you have to use a ram divider? If that's your question then sometimes yes sometimes no. If you ram can overclock 10MHz then there is no reason to use a ram divider but if it can't then yes you will have to.
If the RAM is @ 176 and the FSB is @210 then your already using a ram divider.