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At the moment, I'm not sure if you 'can' wrap the redirect pages within xoops. I've also tried with limited success. You may want to edit the redirect to:
$xoopsTpl->display('db:system_redirect.php');
then make a copy of your system_template.html as a .php file, dumping it in your templates directory and then generating it as usual. IT might take some trial and error, if it works at all.
Again, I have no idea if this will work, but I would try it based what you found so far. I would do it myself and test, but I'm running out the door as we speak.
Others of course may have a better alternative. Personally, I like the redirect the way they are, because they are not affected by the theme.css used, therefor allowing me customize the same consistant look, no matter how often I change my theme. For instance, I use my site logo on my redirect, it's been that way for over a year, no matter what flavour theme my site has used.