I've seen pages in there (Google) with question marks, but in my personal experience they've not been indexed. For instance, this is in there:
ALL the product pages are beyond that, with long dynamic URLs like this (which is now, they were even longer, the shopping cart was just changed):
Not one of the dymamic pages got in, we're doing static pages and I've got spiders disallowed from the entire cgi-bin and shopping cart directory. It's got Front Page extensions installed, so putting something in .htaccess actually brought the site down. No joy with writing the host, either.
I happen to know for sure that Miva can be made flat HTML with some modules or custom coding, but not with FP extensions that I know of. I'd sure like to find out.
I had the same thing on a CF site, where duplicate titles and text were propogated across the whole dynamic part of the site.
Dynamic pages can be dealt with, but in my case if the developer won't/can't deal with it in an existing situation, I've got to work around it. I've seen dynamic pages "occasionally" but not with what I'd try to aim for and not doing well often enough, so I wouldn't take a chance, myself. I'd go for static pages, and if there's a dynamic cart by necessity, keep it separate and parallel and exclude it to avoid duplicates.