No, it's not about the Serializable interface. In the context of web services, serialization means the objects to be transported over
SOAP need to be convertable to XML and back.
If you're trying to send an object Axis doesn't know, you need to configure a serializer to be used. If the object has bean characteristics, you can use the
BeanSerializer that comes with Axis. If it doesn't, you need to implement custom serialization classes.
In general it's preferable to use standard data types only (in other words, not to use custom classes). That gives you a better chance to create a WS that works cross-platform.