Do years in parentheses need to be chronological? Is there a norm that states years of publications should be chronological when cited parenthetically in a text? For example, is the following incorrect?:

"... to that of Mircea Eliade (1964, 1951), for whom the shaman is ..."

I'm revising another author's paper and this is the first time I've ever seen the years out of order. But I can't confirm in any guidelines that it's necessarily incorrect.
The constraints for references are defined by the citation style you're using. If the citation style guidelines do not mention anything about this issue, then it's OK.

Deliberately not using the chronological order seems fully reasonable as it might serve a purpose: In the example, I would assume that the 1964 publication is more informative/relevant in given the context and, therefore, should be named first.