Had you played the game or done some lore research, there'd be no need for me to answer that. They have fertility issues.
I just checked the link you left and that was great information, as it gives population estimates of several towns circa FO2.
If you ask me, civilization doing pretty good.
I think my theory fairly sound, and NCR kinda shows how my population growth numbers would be fairly accurate. Eating legumes for protein would svck, but that is what a verti-assault on a brahmin or bighorner herd is for. Plus rumor has it deathclaw tastes like chicken.
That was basically a rough draft, and Lt you should be proud... I had some Enclave migrate west, explaining the knowledge of RR and ZAX. I also don't have Enclave sitting on butt.
So I found this regarding Vaults:
http://fallout.wikia.com/wiki/Vaults
The key thing is hydro-agricultural farms. I think it would be safe to say the Rig and any other CoG facility would be equipped with these, like I figured they would anyway. If a Vault can provide for 1000, I think RR can.
I kinda like the idea of Enclave wanting to use control vaults to assist in reclaiming America, which is why they sent the all clear signal, but because of the fertility problem, that screwed them in the region.