It does not automatically make it legal, however, you have the options is that correct? Correct. Now it is up to you if you want to be in the first and get money or just to sell their GPU's. Perfectly legal, nVidia pay for the branding end of story. At the end of the day it's nVidia's money on the marketing part, but should it be all them? Just think of it like nVidia is your company, and that is it. Also I highly doubt that nVidia lawyers would allow something that will fuck'em up big time with getting sued their pants of off them.
When a company already has nearly 3/4 of the market and then tells the AIB partners that they can't sell competition parts under their "Gaming" brands anymore or they lose marketing subsidies and inventory priority, you're veering hard toward anti-competitive practices territory.
The choice of:
Keep your 30% of competitor products as is
vs
Jeopardizing your remaining 70%'s supply chain and marketing budget
It isn't really a choice at all.