Currently it's done like this

public void deploy(VFSDeploymentUnit unit, JBossMetaData metaData) throws DeploymentException
 {
 try
 {
 // Pickup any deployment which doesn't have metaData or metaData with ejbVersion unknown or 3
 if(metaData != null && (metaData.isEJB2x() || metaData.isEJB1x()))
 {
 log.debug("Ignoring legacy EJB deployment " + unit);
 return;
 }
...

The problem with this is that if an ejb-jar.xml does not include any namespace (i.e. based on DTD) isEJB2x(), isEJB1x(), isEJB3x() will all return false.
Actually, the absence of ejbVersion should mean EJB2/EJB1 deployment because only these are allowed to use DTD.
ejb-jar_2_1.xsd and ejb-jar_3_0.xsd both define *required* and *fixed* attribute version with values 2.1 and 3.0 respectively.
So, any EJB3 deployment will have a non-null ejbVersion and isEJB3x() will return true.
So, I am going to change the "if" above to

if(metaData != null && !metaData.isEJB3x())
 {
 log.debug("Ignoring legacy EJB deployment " + unit);
 return;
 }