If I understand you correctly, you are asking if a web application can take a regular HTTP request, access a web service to get some data, and format that into the response. All of this in a single request-response cycle.
If that is correct, sure - a web service request is no different from a database request or any other resource grabbing action a web application may need to do.
If you are not talking about a single HTTP request-response cycle then things get more complicated.
Bill
(I just wrote an
article about using JSP to grab an RSS feed - a simple web service)