Put simply yes. The Node.JS / jss-proxy app can run anywhere really, but can most definitely run in AWS, Azure, a2 Hosting, anywhere where you can host JavaSciprt.
For fast interactions with Sitecore between AWS and Azure, you will need to set up a VPN Gateway from Azure to AWS (like a Site-to-Site IPSEC tunnel) for the proxy just to make sure that the Node.JS app can talk to Sitecore through a dedicated route and not rely on just public interfaces when in Connected mode.
Additionally, and for some background, there are no issues associated with running Sitecore in Amazon's AWS EC2 IaaS offerings. And JSS can run so long as you are using the Subscription licensing model from Sitecore, which is the model that Sitecore is encouraging everyone to utilize.