Hi,
regarding the document (see my attachment) suppose that S5120 is not supported in PCM+ software.
The PCM+ is SMB solution primarily designated to manage ex-ProCurve and ex-3Com (support added after acquisition) devices which are now in "E" family of HP networking products. You can see that there are some ex-H3C devices supported in PCM+ but not all.
Ex-H3C devices are in "A" family which is primarily targeted to Enterprise/Data center (of course thats not strict but it is the main idea of E and A family segmentation). For A family portfolio and basically for all HP networking products (and not only HP networking but thousands products of third parties) there is multiplatform HP Intelligent Management Center (iMC) as management software.
It is hard to say if there will be future support in PCM+ for smaller "A" boxes but now its the way as I described. So I suppose that you can discover the A5120 (S5120) but only for basic status monitoring and topology mapping.
Regards Jan