I haven't done a trip on the Rocio Del Mar, but one of my dive partners has. She and the Rocio Del Mar owner are good friends and she's enjoyed her trips on the boat. Last year, she did a lengthy trip when the Rocio Del Mar repositioned in Cabo San Lucas. I dive the Sea of Cortez fairly frequently.
Water temps in July and August will be in 80-85 Fahrenheit degree range (that's 27-29 Celsius). I assume you're doing a Midriff Islands trip. There's a wide variety of wildlife in the Northern Gulf of California and around the Midriff Islands. You have the possibility of seeing big animals like whales (fins and maybe some orcas if you're lucky), sea lions, turtles, dolphins, and whale sharks as well as lots of little stuff like signal bennies and nudibranchs.
Visibility can vary depending upon what's going on. Tidal exchanges in the Northern Gulf tend to be pretty extreme and the currents can really get moving.
-AZTinman