Excellent question. This is the first time I've heard it asked since the new law went into effect. I will say that I think it is incorrect to say that the punishment is $100 fine an no criminal record. An infraction is still criminal, it's just the lowest form of criminal violation that exists.
That said, I highly doubt that an infraction for marijuana possession is going to have an adverse impact on your DUI.
As far as getting this cleared up, my advice is to make a motion to terminate your probation and then make a motion for expungement. This is something my office handles. Feel free to contact me if you have any questions.
Expungement & Traffic
Clearly the best thing for you to do is avoid getting a marijuana citation. However if you should get one while you are on probation for a DUI it likely would not be a probation violation but no one can guarantee that as this is new territory for everyone.