As is tradition with a new event using event style Pokestops, stops that have a grunt remain the same colour (as opposed to getting darker), but still shake. Sometimes it's fairly hard to see just the shaking.
However, the event stops have this small identification on it if it has a regular grunt/decoy/leader/Giovanni. It is some green holly and bells with the 'R' logo on it. It's fairly hard to see from a distance, but it is a distinct identifier.
Hopefully this helps some people find stops for rocket battles for this event!
by Lethargied88