Iain,
This is not branding, this is using your client sites for manipulative purposes to boost SEO rankings and affiliations you have:
Branding is what VB, XF, IPB and most other commercially branded software do, being they place their company name in the footer. That is branding.
You are not branding, you are clearly using your client sites for SEO purposes and other manipulative purposes. Your clients are not buying hosting, so why are they being forced to place such a link on their website?
The last twit to try this out, I personally had a hand in demolishing him and his business through both legal and non-legal methods, so now his site is obsolete pretty much and Google have it listed as:
View attachment 29884
He was doing somewhat worse though than you are, being to randomise phrases through what he so called, "branding" as well.
My point is, please don't manipulate your clients by calling branding, branding, when it's not branding at all. You are intentionally manipulating and using clients sites for your own purposes.
Is the Hivelocity link an affiliate one or do you own that hosting? If affiliate, that is illegal without making it clearly obvious in your terms of sale, and even then, questionable under certain laws within many countries. If they're not directly related to your business and clearly denoted within your license for exactly what they are, also illegal in many countries.
Branding is a link/s directly back to your website under one term, one link... that is branding. You then charge a fee for the person to remove that company link (brand).