Yes and no.
Yes, you can liposuction other areas of the body at the time of tummy tuck.
No, you cannot liposuction the abdomen.
Why? When you do a tummy tuck (this is a full tummy tuck, not a wedge or miniabdominoplasty), you create what is called a skin flap. This interferes with the blood supply to the abdominal skin. You then pull that skin, stretch it, and sew it. This is a lot for your skin to do.
It is not safe to beat up your abdominal skin flap by doing liposuction at the same time. It is too much for it to handle. It is like taking newly laid sod grass and having a football game on it on a rainy muddy day. What would happen to that new grass? Yup. It would die. And that is what can happen to your abdominal skin if you beat it up too much at one time.
Keeping with the grass analogy (go with me here), if you have established older grass, you can have that football game. In the mud and rain. With a brass band. And the grass will live. So 6 months or more after your tummy tuck, go hog wild with liposuction. Your skin is well healed and safe. The new blood supply is established, so it is heartier and can withstand the liposuction with no risk to the overlying skin.
Remember this is cosmetic surgery. It should be safe, avoiding complications, and it should be pretty. Dead skin is never pretty. This concept is well studied in our plastic surgery literature with published scientific studies.