My left foot has the same issue: the pinky toe likes to rest against the 4th toe unless I am walking barefoot. After a few days of wearing the KSOs it stretched (along with the KSOs themselves) and is straighter. I read somewhere that if your pinky toe is stiff even when you try to manipulate it away from your 4th toe it's more than a temporary discomfort and you shouldn't wear VFFs.
You could get one of those toe spreaders (see
http://www.amazon.com/s?ie=UTF8&rh=n%3A11063691&page=1) to train your pinky toe (when not wearing KSOs) to stay put though.
I think the good determining factor is your pinky toe flexibility. If it hurts to move it away from the rest of your toes, it likely is a bad idea to wear the VFFs unless you use the web toe modification or unite the 4th and pinky toe ala Skeletoes (which suck because there's no flexibility for thee toes; I wore them in Modell's and I couldn't believe people compared them to VFFs).
I don't know your foot shape, but if your pinky toe is longer than the toe pocket and is rubbing against the rubber tip, that could be a problem. You could try these mods if you're not worried about ruining the VFFs:
http://birthdayshoes.com/got-morton-s-toe-lengthen-your-vibram-five-fingers-second-toe-with-this-modIf your pinky toe is webbed you could try:
http://birthdayshoes.com/fivefingers-for-webbed-toes-how-about-vibram-four-fingers-modWhen I wore an over-sized Bikila in the running store, the saleslady told me many customer have the same issue as I did where the pinky toe and/or 4th toe don't reach the end of the toe pocket. I then bought a size smaller in KSOs from a different store.