It is possible with restriction. You can use redirects, as many as you want within the scope of the original root domain, which is not the fact in your situation.
For a third party domain the restriction is that only a single redirect is allowed. You should check if this is the fact for your advertisers ads.txt url.
Another possible solution is:
Crawl the advertisers ads.txt and put it in your specific folder once or twice a day.
See the specification:
https://iabtechlab.com/wp-content/uploads/2017/09/IABOpenRTB_Ads.txt_Public_Spec_V1-0-1.pdf
If the server response indicates an HTTP/HTTPS redirect (301, 302, 307 status codes), the
advertising system should follow the redirect and consume the data as authoritative for the
source of the redirect, if and only if the redirect is within scope of the original root domain as
defined above. Multiple redirects are valid as long as each redirect location remains within the
original root domain. For example an HTTP to HTTPS redirect within the same root domain is
valid.
Only a single HTTP redirect to a destination outside the original root domain is allowed to
facilitate one-hop delegation of authority to a third party's web server domain. If the third party
location returns a redirect, then the advertising system should treat the response as an error. A
future version may address other delegation of authority to a third-party web server. Any other
redirect should be interpreted as an error and ignored.