This is the general rule of thumb for NC work: “not primarily intended for or directed towards commercial advantage or monetary compensation.”
That said, it still depends on the artist's (or owner of that asset) intentions. Although there are exceptions, people that explicit marks their work to be used as NC usually want it to be used for studying/reference only, so that could be a conflict scenario. You may have to contact the artist prior to using it to clarify.
Because intent is such a very good word for legal texts... sigh. What were they thinking.
But if the license holder is available, it is entirely possible to ask for a non-nc, or rather "commercial" license. The nc license is usually not exclusive. So they could give out nc for not asking and c if asked nicely (or being paid ;-)
Good strategy.
Even if donation-ware would be considered nc by most, one might want to change business model in the future to premium versions. And with that there would be no discussion about how non c the project would be.
With donation there is at least an ambigous area. It would be easier, if the money aspect would be more fleshed out. Because strictly, even if you do not make profit, your intent was to do so. But intent is hard to prove, so actions have to spell out the intent. (Otherwise you could just claim, ohhh, we never intended to make a profit by selling this hot new rogue like with addicting game mechanics and stunning nc art.) And if you do look at actions alone, giving away a thing for free does not look very profit orientated, or in other words, commercial. Accepting donations does not change this, as there is no obligation.
