I do not believe Rosie O'Donnell is the best choice for a spokesperson because she has a speckled past, but I do believe it is helpful for LGBT rights to promote figures who identify with their cause. Ellen DeGeneres would probably be the better example, in my opinion. These people are like spokesmodels for equal rights.
Often, the celebrities are champions of LGBT rights rather than the other way around. However, for the most part, celebs like Rosie O'Donnel and Ellen Degenerous are positively viewed by the public and are good "role models" for LGBT rights. Rosie O'Donnell, for example, helped to promote LGBT family friendly cruises and vacations and reinforce the idea that non-traditional families deserve safe and accepting methods of travel with their children.
For famous people to assert their beliefs, pertaining to LGBT is not going to help the movement for rights gain traction, but mostly just turn fans against their favorite celebrities. People who already like, as the example given, Rosie O'Donnell, may change their mind about her if she voices support for the LGBT community, if they oppose it. On the other hand, people who like Rosie O'Donnell, won't be swayed to support LGBT rights, because Rosie says so. This is a stupid idea. Average people with extraordinary stories need to be looked to as examples. LGBT won't benefit from celebrity endorsement, but may cause trouble for said celebrities.
No, I do not think there is any way that taking Rosie in as a person to promote any group is going to good for them, and any person like her, that is famous, but is not liked by all that many people is going to help you out at all.
No, I do not believe that promoting LGBT figures such as Rosie O'Donnell and others do not really benefit the right of LGBT persons. This will take time just as the rights of women and African American persons took time. Adjustment and acceptance will come in time; it can not be rushed or forced. More exposure will have little to no effect.