If your service connected vet, rated at 90 to 100, and you are court ordered to a residential substance treatment center?

A treatment program is not an immediate conviction. You are actually being given a choice. Regardless of the amount of time, you would not be considered incarcerated as you have not been convicted of anything.

From the VA Website: https://www.benefits.va.gov/persona/veteran-incarcerated.asp

VA disability compensation payments are reduced if a Veteran is convicted of a felony and imprisoned for more than 60 days. Veterans rated 20 percent or more are limited to the 10 percent disability rate. For a Veteran whose disability rating is 10 percent, the payment is reduced by one-half. Once a Veteran is released from prison, compensation payments may be reinstated based upon the severity of the service connected disability(ies) at that time. Payments are not reduced for recipients participating in work release programs, residing in halfway houses (also known as "residential re-entry centers"), or under community control. The amount of any increased compensation awarded to an incarcerated Veteran that results from other than a statutory rate increase may be subject to reduction due to incarceration.

I would recommend you contact a local VA facility near you for clarification but the key words I see here are: "Convicted of a felony and imprisoned for more than 60 days." I would also ask how long the program is and if you are free to come and go.

While it is court ordered rehab and you are not confined to a cell and if you will have reasonable freedom to walk around. That being the case, I do not see where benefits could be reduced.