No, well you can, but it would be pointless.
NGINX doesn't support keep-alive to backend servers.
It is an HTTP/1.0 proxy without the ability for keep-alive requests
yet. (As a result, backend connections are created and destroyed on
every request.) Nginx talks HTTP/1.1 to the browser and HTTP/1.0 to
the backend server. As such it handles keep-alive to the browser.
(NGINX Wiki)
If you're going to enable keep-alive do it in NGINX to the client, enabling it on the Tomcat side won't do anything if NGINX is sitting in front