Here's a review article which came up when using the following search terms:
Acorus gramineus adverse reactions interactions
I'd caution that some of the chemical structures (and/or their names) in the article are erroneous, which betrays a lack of understanding on the part of the author(s). Hopefully the ethnomedicinal information they present is more reliable. In that respect, calamus is presented as generally safe, despite asarone being highlighted as a potential hepatic carcinogen.
All that says nothing about the potential for interaction with rhodiola, so I'd looking very carefully at how acorus may interact with monoaminergic systems, and exactly what kind of MAO-a inhibition rosavin produces.
If you decide to proceed with the combination it should go without saying that you'd begin with tiny doses and remain vigilant of the effects - all while trying to remain free from hypochondria and other neurotic biases! I can't make any recommendations, but it looks as though the neuroprotective effects of these two herbs may be complementary.