Question: Is Direct Exchange Migration from 2003 to 2010 Possible Without Upgrading to 2007?
Yes. Migrating from Exchange Server 2003 to Exchange Server 2010 is a fully supported upgrade path, and is the simplest way to migrate from 2003 to 2010. There is no requirement to migrate to Exchange 2007 first.
However, something to be aware of is that it is recommended to apply the Exchange 2007 schema update to your Active Directory forest before you apply the Exchange 2010 schema update, even if you do not plan to deploy any Exchange 2007 servers.
By applying the Exchange 2007 schema update first you make it possible to install Exchange 2007 servers later on if you need to for any reason, for example to maintain compatibility with a particular application. Basically it is a fail-safe method of ensuring that if you encounter any compatibility problems with Exchange 2010 you can still migrate away from Exchange 2003 and use a mix of 2007 and 2010 servers instead.