HSO in its original (boxed) form, and also in the form of the VSTi (with 16-bit content) which was the special offer for C5 users, both work as before in C6 … assuming of course you own the correct license!
Yes, and in HALion Sonic SE that comes as part of C6.
For example, if you bought the special offer HSO that came with Cubase 5 and have that license on your USB eLicenser, then you don’t need to do anything else except install the HSO VST Sound Instrument Set from the 2nd DVD in order to get the content. Specifically, you don’t need to activate the trial license from the C6 box because in this case, your existing license covers it.
If you want to use these sounds, you load HALion Sonic SE inside of C6 and select the patches from there (filter on “HALion Symphonic Orchestra” to simplify). You can leave the original HSO VSTi installed if you need to use it from other hosts, or as a standalone.