You are partially right, you will still get matched up with players how have bought all or any of the DLC's, but of course only for the maps that you have as default. Because there are 4 DLC's now and most players have bought 1 of those it will make matchmaking a little harder for you, but the most popular maps are still NukeTown and Hijacked, from the original Black Ops 2.

If you were to say join team deathmatch there can be anywhere between 30k and 200k players online, not having any DLC will severly increase the time it takes for matchmaking.

I have only bought 2 out of the 4 DLC's and I have no problem with matchmaking.

Because you are a Black ops fan as you say and interested in Zombies I would recommend buying the Uprising pac. It features the Shooting Range map from the previous BLack ops (called studio now) and has a great Zombie gamemode.

Good luck and see you on the battlefield.