Adopting a neutral coding style is definitely a good idea. However, only enforcing the coding style when the source is checked in may or may not be a good idea (see also Bill's and Elie's answers below).
Using the check-in hook:
Pro: Allows coders to write however they wish, so they don't have to think about the standard or change the way they write code. This minimizes resistance to the policy, and won't negatively impact their productivity when writing code.
Con: Your coders may have only a passing familiarity with the neutral style, so you aren't getting the full benefit of everyone using "the same" style. If your programmers ever have to work together in a pair programming setup, they are still going to be subjected to one another's programming style on the screen, which is going to be different from their own style or the neutral style.
Going one step further, using the neutral style during development:
Pro: Encourages fluency in the neutral style, everyone can always read everyone else's code before and after it's checked in.
Con: You'll encounter more resistance from your developers doing it this way. Depending on your culture, it could be more trouble than it is worth.