Dear anxiouswife2,
You can definitely let his counselors know. It might help their work with him. And block his number from texting or calling you. He's in rehab, so he's supposed to work on himself, not text you all sort of stuff multiple times a day, especially the mean stuff.
If he starts trying to reach you via other ways and/or you feel harassed or threatened, a restraining order can help. Since he's already not living with you in the same residence, it's a lot simpler - a magistrate can issue the order as quickly as overnight.
I'm going through a somewhat similar situation (I'm on the East Coast, husband going to treatment in CA.) He's been to many detoxes/rehabs before. His texts have also gone across the spectrum basically from "you are an a******" to "I love and miss you so much, more than anything or anyone in the world"; from "I can't believe you've abandoned me" to "You are the best thing that ever happens to me." The change in tone can be so drastic, as much as I've got used to it, I'm still somewhat surprised every time it switches.