This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
There is no way to control the order in which applications in Tomcat get deployed. I tried once.
(Correction, there wasn't when I tried a couple years ago).
One workaround might be to put a context listener in the apps that depend on the SOAP server app. Have it ping that app every n seconds to see if it's running. Make the servlets in the app unavailable until after the SOAP server proves that it's up and running.