In my example I am using JBoss EAP 6.1, although this should be possible with other application servers, I will focus only in BPM Suite 6.0.3 installed in JBoss EAP.
Now after you start BPM Suite the API should be available already and you should be able to call the REST API directly in your code with two warnings:
Notice that this is just the start to explore this generated API. Also, please notice this might expose your BPM Suite installation, so be careful with this feature
Keep in mind that BPM Suite is a product supported by Red Hat and this is not a feature supported by Red Hat, it is my personal experience with the API.