The license is an application-level constraint, not an OS-level constraint. The OS will recognize all the cores which you physically have and which are enabled, and it will recognize cores with SMT as two logical cores.
The license controls how many CoreXL instances you are allowed to run. If I remember correctly, both dispatchers and workers count against this.
Going from four real cores to four hyperthreaded (eight logical) cores yields about a 15%-30% speedup for parallel workloads. This is less than you would get from extra real cores. It's important to note, though, that simply having hyperthreading enabled does not hurt per-core performance, it just gives the OS opportunities to schedule work in suboptimal ways. For peak packet-handling performance, you can enable hyperthreading and use affinity to force your dispatchers and workers onto real cores. Other work can use the hyperthreads opportunistically without necessarily slowing down the traffic processing.