Here's some ideas
You can define a host variable in your ansible inventory file, like this
--
# ansible inventory
# development hosts below here
devdb01 enterprise_manager_port=5500
# test hosts below here
testdb01 enterprise_manager_port=5501
and then create a template dbca.rsp file, where instead of the hard-coded port number, you substitute in the value associated with each host (something like this - i've not looked at the format for dbca.rsp but the stuff inside {{ }} will be substituted
enterprise_manager_port_number={{enterprise_manager_port}}
There are lots of ways of setting up variables in ansible - as well has for hosts, you can do the same for groups of hosts, or have default variables applied to specific roles - and other places too. so its well worth putting aside a few hours to go through the documentation pages and getting an understanding of whats possible.
Hope this helps,
Jon