Awhile ago Tor blocked relays from running on Amazon AWS (after there was an attach that originated from Amazon-hosted nodes). Google GCE was also blocked. See this thread about it from last year when I tried to run a node on google's cloud: https://lists.torproject.org/pipermail/tor-relays/2015-August/007681.html
Yes I remember that thread, but that was some time ago and since I got several emails from ornetradar about someone adding relays on amazon (in IE) in September 2016 [1] I still doubt that amazon or the dir auths are blocking relays from being added there.
you can also use https://compass.torproject.org to find amazon-hosted relays by AS
[1] https://lists.riseup.net/www/arc/ornetradar/2016-09/msg00118.html https://lists.riseup.net/www/arc/ornetradar/2016-09/msg00087.html https://lists.riseup.net/www/arc/ornetradar/2016-09/msg00100.html https://lists.riseup.net/www/arc/ornetradar/2016-09/msg00104.html