It is very nice to see someone ask, but I doubt any of the authors would object, as the rendered visual is always unique depending on the audio, crossover blending, or any added text or textures, and so technically was not created by the preset author.
They can easily protect the reuse of the code that makes the visual, as that is their creation.
The author of Milkdrop itself (Ryan Geiss) could possibly have prohibited its use for public or commercial performance, but that would sort of defeat the purpose of it.
Milkdrop has often been used for public performances over many years, and each time it helps to advertise
, so I doubt very much that Radionomy would even complain if you dropped some hot Llama action in the mix.
Credits is the main thing. Always credit wherever possible. That way people will seek out more, and that will make any preset author happy (unless you use their worst work
).