Updating on this:
I realize this thread became somewhat controversial, but wanted to provide an update. DD9 is still taking the rhodiola and still doing MUCH better. We have had a few minor hiccups on return to school, but overall I would still say her issues are 50-60% improved, if not more. It is, of course, possible that there is some other reason behind this--maturation? Better teacher fit? (she does have a GREAT teacher this year) Alignment of the stars? But it's hard not to attribute it to the rhodiola. We did take a one-week break last month (this is recommended as an occasional "reboot") and it was a harder week than usual.
I have found this page and suspect it is probably overcautious, but am keeping it in mind for any time DD takes other medication:
http://www.sharecare.com/health/herbal-supplements/what-medications-interact-rhodiola-supplements;jsessionid=40F10C30976AE214814B4DD885DE5467
It's really lovely to be enjoying our time with her more and to see her happier.
What is interesting is that DS5's behavior seems as though it had deteriorated since DD has been "better." I almost feel like he notices there is more "space" for him to act out and takes it accordingly. I know her behavior was very hard on him because he used to talk about this and how it made him sad.

In a way this may be healthy so that he has less "best little boy in the world" syndrome, but I worry a little that it may be going too far in the other direction. His behavior at school is uniformly excellent, though.