If your nginx is running as httpd_t putting the socket you're connecting to in /var/run/httpd or /var/run/nginx are two good places to start:
grep httpd_var_run_t /etc/selinux/targeted/contexts/files/file_contexts
/var/run/wsgi.* -s system_u:object_r:httpd_var_run_t:s0
/var/run/mod_.* system_u:object_r:httpd_var_run_t:s0
/var/run/httpd.* system_u:object_r:httpd_var_run_t:s0
/var/run/nginx.* system_u:object_r:httpd_var_run_t:s0
/var/run/apache.* system_u:object_r:httpd_var_run_t:s0
/var/run/php-fpm(/.*)? system_u:object_r:httpd_var_run_t:s0
/var/run/lighttpd(/.*)? system_u:object_r:httpd_var_run_t:s0
/var/lib/php/session(/.*)? system_u:object_r:httpd_var_run_t:s0
/var/lib/php/wsdlcache(/.*)? system_u:object_r:httpd_var_run_t:s0
/var/run/dirsrv/admin-serv.* system_u:object_r:httpd_var_run_t:s0
/var/opt/rh/rh-nginx18/run/nginx(/.*)? system_u:object_r:httpd_var_run_t:s0
/var/www/openshift/broker/httpd/run(/.*)? system_u:object_r:httpd_var_run_t:s0
/var/www/openshift/console/httpd/run(/.*)? system_u:object_r:httpd_var_run_t:s0
/opt/dirsrv/var/run/dirsrv/dsgw/cookies(/.*)? system_u:object_r:httpd_var_run_t:s0
/var/run/thttpd\.pid -- system_u:object_r:httpd_var_run_t:s0
/var/run/gcache_port -s system_u:object_r:httpd_var_run_t:s0
/var/run/cherokee\.pid -- system_u:object_r:httpd_var_run_t:s0
sesearch -A -C -s httpd_t -c sock_file -p write | grep httpd_var_run_t
allow httpd_t httpd_var_run_t : sock_file { ioctl read write create getattr setattr lock append unlink link rename open } ;