Question: Are you referring to using Apache HTTP Server as a proxy or to serve up some static content from a directory on your file system? Then sure.
However, Pega is a Java product and runs on application servers such as Tomcat. Tomcat's web server component is Coyote (java) but it "can" be swapped out. People do configure Tomcat to use Apache HTTP Server instead of Coyote when they want extra speed (although, this may be a myth) or if they want to access non-Java components (Apache HTTP Server is written in C). If any of this applies, then the discussion should continue with your reasons.