Cement Slab ..... If a tree truck is cut very low, is there any reason I couldn't pour cement over it for a dog kennel foundation ?

Yes. Over time the tree roots will rot out and the weight of the concrete will cause the ground to sink in. It might not happen for a few years, but eventually it will happen.

There are SEVERAL reasons you shouldn't pour a slab over the stump. As others have stated, the roots will either continue to push growth, or decay. Even if the stump were permanently stable, WOOD is not a proper base for concrete.

make sure the tree is dead before you lay concrete over it or the roots will split & crack your slab.

Using a chain saw, do all kinds of cuts & cross cuts in the trunk of the stump. Pour a container of salt & motor oil over it & let the tree die before pouring the slab.

Wood rots over time. Eventually when that collapses and can't hold the weight, Fido will be wondering WTF is going on and if there is a major earthquake when his or her house sinks into the ground.

Dig it out, burn it out or grind it down.

https://www.youtube.com/watch?v=6SDyZ8bIly0

https://www.youtube.com/watch?v=7bTpmFGiuZ0