I believe we are clear of liability in this case, since the content is being provided to us with the written understanding that we can use it for commercial work.
Glowforge pays a small fee to the Noun Project on our behalf every time we click on one of those images. So Glowforge is the customer, not the provider.
The Noun Project is going to be responsible for taking down any infringing content, and they are surely aware of it by this point, so as long as the images are in there, they have probably been well vetted by now.
Most of those images, while suggestive of the characters, are not exact replications, and that gets into fair use and fan art and a whole slew of other exceptions, that give me a headache to even start thinking about…that’s what they, (the designers submitting to the Noun Project), would need to hire lawyers for, if anything came up.
(But not us, and not Glowforge. The folks making money off of it are the Noun Project and the original designers.)
Besides, as @PrintToLaser points out…the Glowfolk aren’t jerks. Every time I’ve seen them do something over the last 3 years it has fallen on the generous side of things rather than the venal. (When they can. Sometimes they can’t do it for whatever reason.)
But if we start tracing logos or characters and putting them up for sale without permission, that puts Glowforge, (and us by extension), at risk. It’s just not worth the hassle. Design your own stuff before you try to sell it. That’s my interpretation of what that phrase in the TOS means.