Please feel free to correct me if I am wrong. Chargers for the 620, mini usb, will fit and work on the Hero, ext usb. If, like me, you have an in-car charger for the 620, you don't need to buy another for the Hero. http://www.mobilefun.co.uk/blog/2009/03/htc-chargers-mini-usb-or-ext-usb
Yes they are universal connection, I charge my Hero, PS3 pad, bluetooth headset and digital camera off the same cable.
i suggest you check it as it isnt exactly the same and you may damage the hero's usb conector using them , there isnt a big diferance but it is a slightly diferant shape
Ext USB is backward compatible with mini USB - so chargers etc work fine and will not damage the hero.
I have a USB cable plugged into the front of my BTVision box, my phone get charged overnight of it, and other bit's and pieces are plugged in as and when needed.