That tank is okay, but collareds really need more foot space than height. A 40 gal. breeder type tank wold be better.
You should read a good care sheet, or even several. Yes, they do need UVB, and they are more Semi desert than desert, True desert lizards need much higher temps that would cook collareds. Here are some things that you MUST have to successfully keep collareds:
UVB- I only recommend two types of UVB bulbs.
Mercury Vapor -- Either a Megaray or T Rex Active UVB. These are the best bulbs on the market, but they do produce heat. You have to be super careful about using these on a tank that has a smaller foot space than 36 inches and height of 18 as they can be too hot unless you rig it someway and check temps often.
Reptisun 10 TUBE or Reptiglo 8 TUBE -- These are the only florescent UVB bulbs that I recommend based on studies. But with these bulbs, you need to also provide a good BRIGHT basking bulb, such as a regular bright household bulb or a halogen if more heat is needed.
Temp Gun -- You really have to keep careful tabs on the temperatures in a collared viv, because they need a fairly wide temp gradient. They need a BASKING SURFACE temp of 105-110 to be able to dgest properly, and a cool side in the 70s. The analogue stick on therms and the strips that you commonly see in pet stores can be off by as much as 20 degrees, so please stay away from these.
Here is the best care sheet on collareds, written by our own beloved mod, Eve. Have a good look at it and try to get your viv set up before you get your babies. That will help them adjust. 
http://www.suncharmers.com/id15.html