If you turn off Explorer Replacement mode then Opus 9 should generally work on Vista 64-bit. I agree that it would be good if the installer did this automatically (assuming the installer is able to change the default configuration after detecting 64-bit).
If the TortoiseSVN menus aren't there at all -- not just missing icons but the entire menus -- do they come back if you hold shift when right-clicking the files?
Problems with TortoiseSVN's icons in the file display are usually due to configuration.
It's also possible that you've got the 64-bit TortoiseSVN shell extension installed, in which case it won't work in 32-bit Opus at all (but if it worked in Opus 8 it must be a 32-bit shell extension so this probably isn't it). I see on the TortoiseSVN site that "you can install both the 32 and 64-bit version side by side," which is good.
Opus is Vista compatible, it just isn't fully 64-bit compatible. Same as Opus, and many other programs, are XP compatible but were never fully XP64 compatible. It's just that not many people used 64-bit XP so the distinction didn't come up before but now it seems a lot of people are jumping on Vista 64-bit and noticing problems, not just in Opus but in a lot of things. I have read many stories from non-Opus users who went for 64-bit Vista in order to get more system memory but, after a few weeks, reinstalled with 32-bit because they found so many things didn't work and the things which did work couldn't take advantage of the extra memory.
It will take the industry as a whole a while to get up to speed with 64-bit support. Because Opus interacts with and integrates with many parts of the OS, and because of the way 64-bit Windows more or less segregates 32-bit and 64-bit applications, there will be a few more problems with Opus than your average standalone application.
Having said that, Opus should generally work fine on 64-bit Windows so long as you disable Explorer Replacement mode and are aware that Opus, as a 32-bit process, will be showing you "virtual" views of folders like System32.