HP networking devices from both the ProCurve and H3C stables absolutely are compatible and do work together - that is the great thing about open standards! Readers may have missed the story about HP converting their main datacentres to be Cisco-free: supporting 320000 users worldwide with HP Networking (H3C and ProCurve). The H3C and ProCurve CLIs may be different, but that is what management tools like IMC smooth out. (How many Cisco CLIs are there now...?)
The H3C brand name will remain for China - it is bigger than Cisco, and the brand recognition is too important to lose. All of the newest switches in the Comware/H3C/A-Series stable now have HP branding (physical and firmware) outside China.