In my opinion as GM, it would depend on what the racial hindrance was, and the general feel of the campaign setting.
Racial hindrances are one of the key ways of differentiating between different characters, and allowing players to buy them off could easily end up eroding the sense of individuality between the different members of the group.
They are also different to normal hindrances, simply because they are intrinsic to the very essence of that race. For this reason, I would not simply allow someone to buy them off. However, there are edges that can be used to offset the effects of a given hindrance.
Also, if you start allowing players to buy them off then it can become unfair on certain races. This is because there are some hindrances that it simply makes no sense to be able to buy off. They are then at a disadvantage compared to races where this isn't an issue.
Summary: It depends on the setting, your group and the way you GM. RAW specifically don't allow it (see David Finch's answer for a relevant link), but there are GMs that house rule it so that you can.