Hermes has built its own idea of sustainability into its company - their products are life-time purchases, are built to last and can be repaired, which is offered by no one other luxury handbag/ lifestyle brand. (one of their mottos is: luxury is that which can be repaired) etc
on the other hand, their operations are so environmentally taxing (dyeing hides etc), it might be hard to argue this in a true environmentally friendly fashion. They are, however, the very opposite of fast fashion (willing to give as much time to their designers and creators as is needed) and as such, encourage more thoughtful consumption.
I know other brands' products generally don't have the longevity of Hermes but I've had bags from Gucci and LV repaired by their respective brands as well; so that service is definitely not limited to Hermes alone.
That being said, I think that there are other ways for luxury brands to be more sustainable without having to enter and control the resell market as well. Cutting down on the amounts produced/purchased per year, reducing how frequently we purchase fast fashion (eg. Zara, H&M etc.), types of dyes and increasing the efficiency of processes used in tanning and dying leather, limiting the amount of waste from production and eliminating any run-offs, stringent chemical controls etc. will all contribute to sustainability without adding that much more strain on most designer companies.
Edited: OT: PT