There are lots of FOSS consultancies out there doing fairly well, some linked from the FOSSjobs wiki:

Sure but the open source part is mostly incidental to their work. They solve business needs for corporations.

	▲	pabs3 5 days ago \| parent [-]
		The open source part is usually the whole point, they work solely on open source projects themselves, not deploying those projects for corporations. They work on things like the Linux kernel, mesa, systemd, distros etc.