If it is made available to Tiger users, it'll be posted to Software Update.
Whether or not it will be available to Tiger users is not clear. In fact, it's a question I've been wondering about.
Safari 2.0, for example, is exclusive to Tiger; Panther users are stuck at 1.2. At no time has Apple promised that the final Safari 3 would be available for Tiger. (In the WWDC keynote, Steve said there were "three versions" of Safari...One each for Leopard, XP, and Vista. No mention of Tiger.)
On the other hand, it seems wrong that Apple would make the final version of Safari 2 available to Windows XP users (a six-year-old OS from a competitor) and not to users of a two-year-old version of their own OS.