Can you explain why it's prohibited here? If this is allowed in littlewhitey's server, and as we know is a very old and official server, I do not see the least reason.
Alright then, let me explain. There are arenas where players climb palm trees to gain a better tactical position and to better avoid being noticed (for example, the palm tree near the Ryton Aide pharmacy in Little Haiti). Players with the greenless mod can easily spot these players on the trees while players players who don't use the mod can't spot them as easily, and I don't want to turn VC:MP into a competition of who has the best mods. There's also the case with the bushes. There's arenas that use the bushes to block the view in certain spots, and players with the greenless mod can see through them, which isn't very fair. As you know, we also create create custom arenas and if we were to create more arenas which make use of the "climbable palm tree" or the bushes, players with this mod would have an advantage.
Those are the reasons why I dont allow the mod here, I can't speak for LW and their reasons for allowing the mod, since I'm not part of the staff, but I can say that LW's rules do not dictate this server's rules.