Roc,
You have to claim all foreign sources of income on your tax return, including interest from savings accounts. Depending on your personal tax situation, you may be eligible for certain deductions which will reduce the amount of tax payable.
If you don't declare the foreign interest income, will the CRA find out? There is always a possibility given that you can only make deposits with cashier's cheques, bank drafts, wire transfers, etc… all of which leave a paper trail. If you're just a regular investor (i.e. don't transfer millions each month), chances are you'll get lucky as the CRA doesn't have enough staff or resources to check everyone out, but the CRA does do random spot-checks, and if you're unlucky enough to get caught… you better get a good lawyer.
As far as the interest rate, 5.5% is pretty good for a one year GIC, but keep in mind that a lot of these offshore banks have hidden fees that eat into your profits. You really need to do some digging to find out whether they have monthy "maintenance fees", whether they have a special "surcharge" for non-resident accounts, whether they charge fees for incoming wire transfers, etc… and do the math to se eif it's worth the hassle to open an offshore account.
You also mentioned the one thing that keeps me away form these accounts: no deposit insurance. If they go belly up, or even if they give you a hard time when you try and transfer your money out of their accounts, good luck trying to get anything done by telephone. You'll have to hire a local lawyer to go to bat for you, and if you get screwed by the local lawyer, you have no recourse.
I'm sticking with the 4% GIC's available here in Canada.