If you mean iCloud Photo Sharing, It will share the Photos and they can be downloaded to other devices.
iCloud Photo Sharing FAQ - Apple Support
As to your second question, since the iPad is not really designed as a laptop replacement, you will find it cannot do many things that are natural on a laptop. USB drive support is one of those things. The iPad does not have a USB port. And even using the Camera connection Kit's USB adapter will only really let you transfer Photos and videos on the hard drive and onto the iPad that are stored in a very particular way. (as If a camera had created them) You cannot access the hard drive file structure like you would on a laptop. And you cannot write directly to it form the iPad to store files.
Also if the external hard drive does not have its own power source, the iPad will not be able to power it and will issue a warning about it.
If you needed laptop features, a Macbook Air would have been a much better option for a very similar price.
There wireless hard drives however, that can work with iPads, and to read and write files to and from them, but use their own custom App to do so.
http://www.seagate.com/external-hard-drives/portable-hard-drives/wireless/wirele ss-plus/
http://kb.sandisk.com/app/wireless/session/L3RpbWUvMTQ0ODU1MDExNi9zaWQvLXg0V3Z0Q 20%3D