With BigFix platform 10.0.8+, http call redirection is followed; if the destination is HTTPS, the connection will be validated with certificate before the download actually happens.
This does not address the case where HTTP calls are blocked in the network (in which case they do not reach the destination server, so no redirection happens.
In this latter case, currently you can either manually pre-cache the content on the Root Server, or change the actionscript to use the https address in place of http.
BigFix will work going forward so that https URLs are used where available.