Aruba controller has a ALG for vocera so it should able to detect it from a firewall perspective , make sure that on the SSID you have the lower data rates enabled
There's already a Vocera ACL available on the controllers:
Make sure you read this document which has some good tips to allow Voice devices to roaming appropriately on wireless:
http://www.arubanetworks.com/wp-content/uploads/DG_Roaming.pdf
http://www.arubanetworks.com/techdocs/ArubaOS_61/ArubaOS_61_UG/Voice_Video.php
And also Vocera has best practices to work properly on wireless :
http://www.vocera.com/products/documents/InfrastructureGuide.pdf