First of all - a resource adapter isn't a datasource.
If you want to limit account access per server, and you know the account names up-front, just do a <config-property> on the ManagedConnectionFactory with the account names in a "," separated String. Then verify the CRI information against that. And the pool will be divided based on the equallity of the CRI, so there is no "same pool".
Read http://docs.jboss.org/ironjacamar/userguide/1.0/en-US/html/introduction.html#overview_outbound - and look at http://docs.jboss.org/ironjacamar/userguide/1.0/en-US/html/samples.html#sample_helloworld