Having looked at the code of tomcat6-embedded container and the code of org.apache.catalina.startup.Embedded

https://github.com/arquillian/arquillian-container-tomcat/blob/master/tomcat-embedded-6/src/main/java/org/jboss/arquillian/container/tomcat/embedded_6/TomcatContainer.java

// creates an http connector, i.e., <connector> element in server.xml

Connector connector = embedded.createConnector(InetAddress.getByName(bindAddress), bindPort, false);

I figured out that Http connector in Arquillian environment is always blocking