I'm assuming you mean proprietary code generators handrolled for specific in-house use since otherwise anything short of machine code is a code generator. But here you go:
I think it's very arguable that the node graph in Blueprints is easier to maintain and far less error-prone than the GLSL/HLSL code it generates (and would have otherwise needed to be handwritten).
It's also so much more productive to come up with new shaders since you get a realtime visual feedback of how the end result looks like as you change the graph. I'd definitely prefer to maintain thousands of shaders represented with nodal graphs this way instead of GLSL/HLSL code, and I'm actually more familiar with writing GLSL/HLSL than using Blueprints. I think it's actually practically impossible to cause like a major bug besides maybe some minor visual glitch you'd probably catch right away because the "visual language" imposes sensible constraints with often a pure functional style that doesn't allow you to, say, crash a shader, at least AFAIK (I'm admittedly not an expert with Blueprints).
There's not even "code" to maintain anymore. You just place nodes inside a graph and draw links between them and, voila, it generates shader code for you. Who maintains this stuff and says, "You know, my life would be so much easier and I'd have so much more free time if this was just written in GLSL code instead of using Blueprints." Probably never.
That said, I have run into my share of proprietary code generators that did make life harder, making me learn this stupid meta language that has very limited benefits, if any, over writing code in the language of the code it generated. To me a tell-tale sign of code generation that's shite is one that does little more than reduce a small amount of boilerplate and doesn't actually reduce, say, the possibility of bugs. You know it's especially shite if it actually introduces new ways to cause bugs that the original language didn't have. But there are cases for code generation, like the above, where the productivity boost is so massive, rendering meticulous things that cost enormous time now cost pennies, that no one would ever use it and then look back.
To me there's a more legit argument for the proprietary development of Blueprints among the Epic team than many superfluous programming languages out there made for the general public which barely bring anything new to the table.