Reviewers can create ideas from within in Aha!, but can't edit them or vote on them from within Aha!.
For public ideas, a reviewer can go to the public portal and vote and add comments -- this helps. But for ideas that are not viewable in the portal, they cannot vote or change their description (although they can comment under private comments).
As mentioned, reviewers have many capabilities in Aha! - They can create ideas, add comments and complete to-do's. The thought in mind for Reviewers is that they are more of a "reviewing" type role vs. a more active user like a Product owner or contributor.
As also noted, reviewers can go to the public portal to vote and comments. However, they are able to do this on the public portal - not because they are Reviewers, but because they are public users of the portal itself.
We have spent a lot of time with our customers to define the Aha! roles and permissions and we are unlikely to make changes in this area. I hope you can understand.
seems an oddity the way it is!