[PrO.GameR]

As far as I read somewhere one of the players complained everytime an object loads a custom material server sends every data about that object up to that material.
So basically it'd be something like this (don't quote me on this, read it long time ago but should probably behave almost the same)

Object data packet sent.
Object data + custom material index 0 sent.
Object data + custom material index 0 + custom material index 1 sent.
...

If thats still how it works then using too many textures on too many objects might lag, but still shouldn't be something the network can't handle.

After load they behave normal, until they get unloaded by streamer and reloaded later again.