Check this:

Got to Preview > Split Screen View icon > confirm you HAVEN'T engaged the FX-Bypass option and then HAVE engaged the icon.

2 options here:

1] Engage the FX-bypass when it IS selected

or

2] Disengage the FX-bypass when it ISN'T selected

Both of these option get you the same result: No FXs being seen working in Preview.

Pros: A powerful & valuable feature set allowing an editor to ascertain if you are getting the FX result you want

Cons: Does require a modicum of appreciation just what Vegas can do.

So,the "Problem with Swirl Video FX on vegas pro 8 ", if this IS the case, FX By pass Icon User error, and I think it will be, wont be an issue with this or, come to that, any of the Vegas FXs.