The website I am working on uses an image defined in CSS as the main logo. The html code looks like this:
Something.com | The best something ever
You should be fine with visibility: hidden.
That said, if your image is part of the content (and I would dare to say that a company logo is content, not presentation), and you care about accessible html, you should consider changing your code to include the image as a img element with title and alternate text, instead of a css background-image.
Additionally, if you hope to attract search engines to the keywords inside the element, you might want to include those words more than once in the page. The page title is a much more relevant place than the h1 element, for example.