The best way to know is to implement an example web service and try it!
If you wonder whether you can return something as a result of a web service method or whether you can use some parameter type, then ask yourself how you would represent that data using XML.
An array of strings can be represented as an element with maxOccurs larger than 1. The result would also have to be wrapped, since the WS-I Basic Profile only allows the SOAP body to contain one single element.
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Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop