Yes, it is possible and of course legal to use WildFly in production environment.
However, to get fully tested, supported version, Red Hat offers "JBoss Enterprise Application Platform" which is the commercial offering, see Red Hat JBoss Enterprise Application Platform | Red Hat
Additional to Rado's comment I would not recommend to use AS7 as this version is quite old.
If you try to use the community version in production I would use the latest version to being able to get the latest fixes.
If you need a reliable version, patches and security updates for a longer time you should consider the EAP version as mentioned.