He absolutely needs to get a lawyer, and they likely will be seeking to revoke his probation. Because his original offenses involved driving, they will likely view his driving in violation of the conditions of probation to be a major offense. This offense, combined with recently failed drug tests, suggest that he does not have any respect for his parole and that he will likely reoffend in the near future. Most parole officers would consider him to be at serious risk at this point.
Texas does not have house arrest. In some cases, parolees are put in a super intensive program instead of being revoked. However, I do not believe that such is common with alcohol related offenders (who are often given serve-alls - which means they are required to serve the balance of their sentences.)
Bottom line, he needs a lawyer.
The best advice you can take away from having asked your question is that: Your roommate needs to get a lawyer!
There is a lot of discretion in these situations and a good lawyer will cast this cast in the best light for your roommate.