Can I plug my Iomega hard drive into my new BT Home Hub and access the tunes stored in it from my MacBook Pro wirelessly?
You can connect a USB hard disk to the home hub, and access it as an SMB network drive. There are instructions on the BT website.

You would be able to open your iTunes library from the network drive, but the home hub doesn't have an iTunes server built in (or at least the v2 I have doesn't, and I can't see any mention of it in the v3 features) so it won't appear as a shared library in iTunes. 

Make sure the drive is formatted to Fat32 and it's basically plug and play.