The comments about GPL FUD seem a bit odd to me. The reason companies aren’t generally worried about Linux being GPL, but were worried about ZeroTier being GPL, isn’t because Linux is “grandfathered in”. It’s because these people aren’t confused about how the GPL’s viral nature works. As described lower in the article, companies are looking to incorporate ZeroTier code as a part of their custom, proprietary tool, which would cause the GPL to apply to them (that’s the whole point of the GPL: requiring them to share if they start shipping something like a VPN client binary which is powered by ZeroTier code).
Companies with a “no GPL” policy are pretty much always ok with a commercial license for a codebase that also has a GPL license, from a purely license/freedom standpoint. But also in almost all cases, it’s way more work/effort for a dev team to get a commercial license than to use a non-GPL open source library, because they have to coordinate with legal/procurement teams.