Yep, you just need to sign into Cydia with the same id you used to buy the app in the first place, and then click Manage Account for a list of previously purchased apps you can then re-download for free.
Sure...one thing to note is that some devs limit your licenses to one device. Others let you use it on two--something to keep in mind in case you want to use something on an iPhone and an iPad, or on a newer iPhone, etc.