Got no problem with him going to FCW first and he shouldn't either. He's never been in the WWE and has never wrestled in their ring. He needs to get used to their style first and work with some of the talent there and get advice from some of the legends helping out at FCW. Put him there for a short while but not very long. But I don't really know tbh. I somewhat don't think he needs to go to FCW, he's fine as he is but I think it always helps going there first. But if he is to sign with the WWE, wouldn't it be better to have him go straight onto their main roster debut on WWE TV first? Everyone is gonna see who he is at FCW and dark matches which would ruin it but he isn't that big of a name so I dunno.
In particular one guy who didn't go to FCW and went to straight to the WWE roster is Sin Cara. He is a great wrestler but he had trouble adapting to the WWE style. But then again, Mexican wrestling is completely different to American wrestling and TNA is similar to WWE so yeah it would be easy for Shelley to adapt to WWE. But once again, ADR was a Mexican wrestler and it was pretty easy for him to adapt to the WWE style.
My final opinion: Straight to the main roster.