Can Microsoft's IIS Express and SQL Express servers be implemented for a small web application in production environment?
What is the limitation of them?
SQL Express
Yes. This – small server – is its target use case.
IIS Express
Given it requires an interactive user session: no. And that's assuming no licence issues.
But why would you want to use IIS Express? On every machine you can run IIS Express you have IIS available.
You should just ensure that iis has been enabled on the web server you're planning to use. It's there for sure just might not be activated. No additional license is necessary.