It depends on what you’re taking about. If you’re asking about managing a large scale system with scaling and such, Discourse does things in a unique way and you’ll probably want a Discourse expert. To start, though, a standard install on a beefy server should serve you well until your community is generating money. You’re not going to have thousands of users over night.
As far as customization is concerned, it’s probably not ruby that’s so important but css, ember, and javascript. Your php guys will likely need a bit of work to get up to speed.