When it comes to LoadUI, then under the hood it depends on what component you are using to generate load:
Webrunner:
http-clientGebrunner: Whatever
geb-script you provide
SoapUI-Runner:
the SoapUI engineYou could probably loadtest the functionality of your Ajax-applications using Geb-runner inside LoadUI.
LoadUI is, however, built primarily for loadtesting API's.
If you want a product more adapted to web-testing, you can checkout our partner product, [urlhttp://webloadui.org/about/why-webloadui.html]WebLoadUI[/url]
Best regards,
Mikael
The LoadUI Team