I am considering buying a pasta pot, such as the All-Clad 6807 SS Copper Core. Can I remove the colander and just use the main body to cook tomato sauce? Or can it only be used for water-based cooking?
"Pasta Pots" for the most part are just pots that come as a kit with a fitted colander and a lid which make cooking pasta easier. In 99% of cases they are not exclusive to cooking water based cooking methods, and for the rare exception it would be plainly marked on the packaging when you bought it (if you didn't look, check online for resources either from the retailer or manufacturer).
The difference between a "pasta pot" and any other saucepan is merely that the colander is integral. You don't have to go find a colander & pour the water/pasta out through it, you simply lift out the integral colander ... of course, you still have to find somewhere it can drain & you still have to throw out the water afterwards.
Net gain, not a lot, unless you're running a restaurant.
You can use the integral colander for anything you would boil then separate from the water afterwards.
All-Clad's own site - ALL-CLAD COPPER CORE® 7-Qt Pasta Pentola...
All-Clad's pasta pentola, a 7 quart stock pot designed with a colander insert, enables easy lifting and draining of cooked pasta. This essential pan may also be used for steaming and blanching a variety of foods, including vegetables and shellfish. Additionally, making stocks becomes effortless by adding meat, seasoning and other ingredients to the insert which is then simply removed when finished, eliminating the need for straining.
Remove the integral colander & it becomes just a saucepan.