The picture is a little fuzzy but trust me when I say I'm pretty sure I know how nasty his lesions must look since I've seen my fair share of them over the years.
The area will be infected if there's a distinct odor so you won't want to use any steroid ointment or cream on it. Otherwise, the approach will be very similar to the other client you had:
1. Clip up the fur as you have done.
2. Gently clean with dilute betadine or iodine (not full strength since it will burn).
3. Spray with Vetericyn several times a day. After dry, apply antibiotic ointment.
4. Make sure to use a harness instead of anything around the neck, especially the shock collar. This may be obvious to you but you might be surprised how many owners would still use a collar in this situation.
5. Aspirin could be given to help with inflammation/discomfort at a dose of 10 mgs per pound of body weight twice a day with food as long as Kaiser isn't taking steroids or other nsaids. For example, the dose for a 60-70 lb dog will be 2, full strength 325 mg tablets at one time.
If the infection is deep, though, he may need systemic antibiotics; topical treatment may not be enough. You (or they) should know in a day or so if it's healing, worsening or staying the same. If the last two scenarios, then a vet visit may be prudent.