I am not sure what switch or code you are using, but typically you need to use "mls qos vlan-based" to make that policy on the VLAN interface active on both ports. The answer though is yes, these two interfaces will share that same policer as one 10Mb/s pipe.
If it's CatOS, it works the same way as far as the concept, except the way you apply a "policy" (qos ACL) is obviously different.