The list of connectors changes more often than the current PowerCenter version and hotfix. ;-)
Please check with your Informatica sales representative, they have the latest lists of available license options and can tell you how much you would have to pay for each kind of connector.
In what way do you want to exchange data with HCM?
What kinds of interface does HCM offer? Maybe they have an easy web service interface, or there's a Java or C based API to bulk-load or bulk-extract data?
Kindly note that Informatica PWX connector for HCM is not available for IDQ or Powercenter as of now. Only IICS connector is available at the moment as you rightly understood.
I don't know ICS or IICS good enough to judge that myself, but I dare to guess that from IICS it should be possible to invoke command tasks (such as calls to pmcmd). That means that you could use IICS to connect to HCM to extract data from there and stage them e.g. in a relational database or some staging flat file. Then use PowerCenter to process these staging data and to deliver return data via some staging table or file. Finally you can use IICS again to return the results to HCM (if necessary).