thats certainly not my understanding of how the DM's guild works. I thought it gave you permission to use WOTC's IP a quick google shows loads of products on DM's guild using Drow and beholders, here is just one example
https://www.dmsguild.com/product_inf...57&language=en
while this page explicitly gives you permission to use tthe beholder stst block or any other official 5e NPc as long as you publish via the DM's Guild
https://support.dmsguild.com/hc/en-u...-OGL-Questions