Yes, any webserver that provides “X-Frame-Options” in the header of their response won’t work in the webviewer of a web published app. This is a restriction on putting websites in a frame for security purposes: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
The Baker Technology site has “x-frame-options: DENY” for example, which doesn’t allow the page to be put in an iframe.