I'm not a lawyer, but I'm pretty certain that's not how the GPL works. It has no effect on the content you create using the tool. It places restrictions on redistribution of the code itself. I don't think there are any limits on what you do with gimp or blender, unless you are modifying its code and redistributing it.
Yes the GPL doesn't apply to work created by GPL software. I've heard people in companies be worried about it though because they misunderstand "using GPL libraries" as applying to work created as a product of them, rather than strictly software.
The Blender Foundation is quite upfront about this though to prevent misunderstandings. It's directly addressed on the page that explains the license: https://www.blender.org/about/license/
That is correct, but there are plenty of lawyers who interpret things incredibly overly-conservatively to save their own ass, just in case.
If you're a senior enough manager and have a legitimate business reason then you can often push back enough and get them to give in, but it's really a question of whether it's worth your time and effort internally.
