Absolutely! Boxing can be a highly effective cardiovascular exercise to really get the heart rate elevated.
A very common misconception is that cardio has to necessarily use the lower body. Not so. If you are training to elevate your fitness and/or enhance fat oxidation (or fat loss), any cardio that you perform that elevates your heart rate is going to be highly effective.
Boxing is a great example. You can perform a great high intensity interval workout with boxing alone. If you want to try a demanding interval boxing regime, try this: 30 seconds all-out, 30 seconds slow and easy, repeated for 20 minutes. If you give it your all, you will be exhausted by the end of the cardio session!
Here's the key to great results - perform a format of cardio that you enjoy. If you really like boxing, then stick with it. If you enjoy it, chances are that you will get the most out of each session, whilst also increasing the likelihood of long-term consistency.