You are right in saying Vanaras do not have weapons and maces are for glorification. Using boulders and trees is their choice. There is no rule that they should not use any physical weapon.
As Vanara means a forest ranger, they are highly likely to use trees, boulders as weapons. They are skilled with weaponry but they chose to use trees and mountains. I explained it in an answer of mine to What is Lord Hanuman's weapon of choice from scriptures?.
All of them are the assaulters with stones, and all are the attackers with trees, and all have their nails and claws as their weapons, yet all are experts in missiles. [Balakanda 17-25b, 26a]
They mostly picked up boulders and trees as they are the weapons which they find easily available. We can say that because Hanuman used an iron rod to kill some Rakshasas in Lanka.
Surrounded on all sides by those strong demons, that Hanuma endowed with a great strength seized a huge iron bar belonging to the arched gate. Taking that iron rod, Hanuma killed the demons. That violent Hanuma strolled in the sky, taking that iron rod in his hand, as Garuda the eagle would carrying a serpent in its claws.[5-39-40]
In the war between the Vanaras and Rakshasas, Sugriva, the lord of vanaras, picked up a n iron rod and steel club from the earth surface and hurled it on up on Mahodara.
The valiant Mahodara, who was the tormentator of hostile forces, lacerated Sugreeva with his arrows. That enraged Sugreeva then saw an iron rod on the ground. Swinging that flashing iron rod and showing it to him, Sugreeva killed the excellent horses of Mahodara with that iron rod of terrible speed. [Yuddha Kanda Sarga 97 shloka 16,17]
Thereupon, the spirited Sugreeva took hold of a formidable steel club, entirely decked with gold, from the earth-surface. [Yuddha Kanda Sarga 97 shloka 23]
These weapons club (Musalam), iron rod (Parigha) etc., are not Sugriva's weapons said to be used by Rakshasas several times in the Valmiki Ramayana.
So, it is their choice which weapon to use and fight with immediately. They pick the immediate weapon to fight their opponent. They don't specifically own weapons.