After struggling for days, I found this solution:
Don't connect to your database through a datasource defined on your wildfly. Instead, in your persistence.xml:
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="org.hibernate.events.jpa" transaction-type="JTA">
<properties>
<property name="hibernate.dialect" value="org.hibernate.spatial.dialect.postgis.PostgisDialect"/>
<property name="hibernate.connection.driver_class" value="org.postgresql.Driver"/>
<property name="hibernate.connection.url" value="jdbc:postgresql://localhost:5432/yourdatabase"/>
<property name="hibernate.connection.username" value="username"/>
<property name="hibernate.connection.password" value="password"/>
<property name="hibernate.connection.pool_size" value="5"/>
<property name="hibernate.show_sql" value="false"/>
<property name="hibernate.format_sql" value="true"/>
<property name="hibernate.max_fetch_depth" value="5"/>
<property name="hibernate.hbm2ddl.auto" value="update"/>
</properties>
</persistence-unit>
Because the early 5.0.x versions of hibernate apparently had no proper integration of hibernate-spatial and to avoid classpath problems, I added the file jboss-deployment-structure.xml to my META-INF:
<?xml version="1.0" encoding="UTF-8"?>
<jboss-deployment-structure>
<deployment>
<exclusions>
<module name="org.hibernate" />
<module name="org.postgresql" />
</exclusions>
</deployment>
</jboss-deployment-structure>
This will prevent the wildfly provided hibernate to be used by your deployment so that you can instead add a dependency for the most recent hibernate version (5.1.0 as of this writing). You will then need to add dependencies for hibernate, hibernate-spatial and postgresql-jdbc.
Also note that hibernate 5 doesn't require the @Type annotation anymore.
I have managed to get my project working with the settings above and one of my entities featuring the following attribute / column:
@Column(columnDefinition = "geometry(Point,4326)")
private Point position;
I hope it helps, good luck!
Edit:
Using this approach, you need to add your postgresql jdbc driver as a dependency to your project.
Edit:
I have prepared a working sample project demonstrating the use of wf10/hibernate5/postgis - check it out on github:
https://github.com/Pulvertoastmann/wf10postgis/