On the catalyst 6500 switches, the maximum number of HSRP group IDs are limited to 16 in the Supervisor Engine 2-based systems. This limit is 256 in all other older and newer systems.If you try to create a new standby group after this limit you recieve

More than 16 standby groups not supported in this platform.

message.Cisco says that this is a per interface limit. So, you can use same ID in several interfaces.

You can find the details on “HSRP Group Limitation on Catalyst 6500/6000 Series Switches Frequently Asked Questions”