this module do not change any links on the page and not makes modification in the HTML output,
AND the search bots not use this module (because cannot), so they not see these pages
so I see no any SEO trouble, related to this module
It is similar to the default breadcrumbs in that it provides breadcrumbs - but that's where the similarities end. The breadcrumb markup is radically different to the standard output.
Yes, the alt attribute for separator images is set, and is set to an empty value. Empty alt values for breadcrumb separators (Joomla default) are perfectly valid HTML.
Alt-text is a way of communicating relevant information contained in images to people who cannot access images. However, not all images are relevant to nonvisual users. When images are relevant only in a visual context, provide blank alt-text (alt="") so nonvisual users do not have to bother with irrelevant content. Software that reads Web pages understands that empty alt-text identifies an image that is irrelevant, and so it does not communicate any information about the image to the user.