It may seem like the misdemeanor charge should be subsumed by the felony disposition, but the law says otherwise. The misdemeanor judge has the ability to give your brother up to one additional year of probation or up to the maximum time in jail he got when he was originally sentenced (and put on probation). The misdemeanor judge may be upset that your brother did not get a prison sentence and may want to punish him with as much county jail time as he or she can.
Contact your brother's lawyer to discuss this matter further. He or she will be in the best position to explain what is likely to happen in this particular judge's court.
Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.
Unfortunately, no. The felony charge which your brother signed for is a separate criminal charge against your brother. The misdemeanor DWI probation revocation is a completely separate case with its own consequences wholly independent of the felony.
If he has already signed for probation on the felony, there are really three potential outcomes on the misdemeanor. First, the revocation could be dismissed outright, but that is unlikely. Second, he could sit out his misdemeanor revocation in jail for up to 1 year in county max, and have that probation terminated. Third, his misdemeanor probation could be amended, meaning that he would be placed back on probation on the misdemeanor with additional terms (concurrent with any felony probation terms).