If it helps anyone, I was able to get a disabled button to show a tooltip by simply putting a span inside it and applying the tooltip stuff there, angularjs around it...
<button ng-click="$ctrl.onClickDoThis()"
ng-disabled="!$ctrl.selectedStuff.length">
<span tooltip-enable="!$ctrl.selectedStuff.length"
tooltip-append-to-body="true"
uib-tooltip="Select at least one thing to enable button.">
My Butt
</span>
</button>