Can an outdoor receptacle be supplied through a GFCI in a bathroom?
This isn't "dangerous", but it can be inconvenient when your outlet goes dead and it's tricky to figure out where the GFCI reset button is.

On the other hand, this could be against your local electrical codes. For example, NEC 210.11(C)(3) states that your bathroom circuit may only power bathroom outlets. Note that there is an exception to this rule: When the circuit supplies one bathroom (i.e. isn't shared between bedrooms), other things (such as fans and lights) in the same bathroom can share the same circuit. Regardless, the mentioned situation is against the NEC code.

As to if the builder should modify this, I can't say. When in doubt, call your local building inspector.