I am not sure why Google would be seeing redirects. bbPress only redirects after form submits via wp_redirect to the best of my knowledge. Some plugins do too, but usually again after only form submits. Even tag URLs don’t use redirects.
Are you saying the sitemap plugin does not generate permalink urls but rather the non-slug type ie.
?topic=123 If so, it’s outdated and if you are using slugs it should be modified to generate results that take advantage of slugs.