You have essentially 4 options with GC and Aloha (and for most first or second tier POS systems for that matter):
1- You can manually maintain and track your own gift certificates and just tender them out to GC on the POS. Pain the azz, but you don't have to buy anything. (all paper based, but I do know some clients who still do it this way)
2-You can get the stand alone variety GC that you will need to purchase from your dealer, which allows your assign amounts to cards and does all the tracking.
3- You can get the enterprise version of the GC, which allows customers to check their balances online and tracks their use between various stores if you have more than one location. However, I have heard clients complain about "per swipe" charges from Radiant, as well as having to buy cards from them and them only.
4. There are a number of 3rd party options available to you, such as stand alone machines. But also software based ones like OPTINET which works pretty well with Aloha, that you buy directly from them. You can also check balances online, and get a lot of the enterprise version features without the Radiant prices.
If you're a single store, I think option 2 or 4 is your best bet.