In our previous work with cfajaxproxy, we never attempted to pass an array as an argument to a remote CFC. We've since encountered a use case for this and it was much easier to just change the behavior than to go plumbing through the AjaxProxy extension, but I wanted to report our findings anyway:
In Lucee, every element of the array is mapped to a struct key with the index of the array as the key and the value of the array element as the value, e.g.:
EDIT: Details and fix are both in the comments.