Is there any way of retrieving a list of poll voters from Instagram stories?

Yes, but not using the Instagram Platform API (via https://www.instagram.com/developer) but rather the new Instagram Graph API

Your account must also be a business account or else you won't have access to the end point.

The endpoint is: /user/stories and can be found in the following documentation

I hope this helps someone, I wasn't able to find a good answer so here's to knowledge-filling.

To be honest I'm not familiar with the Instagram API,

I tried to find the AJAX request on my story, and find out that it is as follow:

https://www.instagram.com/graphql/query/?query_hash=<_QUERY_HASH_>&variables=%7B%22reel_ids%22%3A%5B%22<_USER_ID_>%22%5D%2C%22tag_names%22%3A%5B%5D%2C%22location_ids%22%3A%5B%5D%2C%22highlight_reel_ids%22%3A%5B%5D%2C%22precomposed_overlay%22%3Afalse%2C%22show_story_viewer_list%22%3Atrue%2C%22story_viewer_fetch_count%22%3A50%2C%22story_viewer_cursor%22%3A%22%22%7D

'variables' is just a URL encode of:

{"reel_ids":["<_USER_ID_>"],"tag_names":[],"location_ids":[],"highlight_reel_ids":[],"precomposed_overlay":false,"show_story_viewer_list":true,"story_viewer_fetch_count":50,"story_viewer_cursor":""}

Note, you need to replace <_USER_ID_> with your user ID, And for me <_QUERY_HASH_> was some constant string,

Then, the response JSON can be parsed using a small Python program:

import json

def parse_instagram_json(json_as_str):
    data = json.loads(json_as_str)
    if ("data" not in data) or ("reels_media" not in data["data"]):
        print "Invalid JSON"
        return
    for media in data["data"]["reels_media"]:
        for media_item in media["items"]:
            print "You have {} views".format(media_item["edge_story_media_viewers"]["count"])
            viewer = []
            for v in media_item["edge_story_media_viewers"]["edges"]:
                viewer.append("{} ({})".format(v["node"]["username"], v["node"]["id"]))
            if 0 < len(viewer):
                print ", ".join(viewer)

I'm not sure if I'm getting the viewer list or the voter list,

The JSON fields suggest it is the former but you can give it a try and maybe it will be what you was looking for...