Yes, we do this when taking payments for example.
Take a look at the iFrame Component module in the Marketplace.
https://marketplace.mendix.com/link/component/117308
Hi
You can also use html/javascript widget from marketplace:
https://marketplace.mendix.com/index3.html
Regards
Yes. Beware: the other party does have to allow your app to wrap their page/site in an iframe.