After doing a thorough search in the Spanish press (including Gramma internacional), I haven't found any indications of Cuba's official support of the Kerry campaign. It is obvious that Kerry is the preferred candidate, but Cuba remains very cautious at this point.
Democrats may not use the same hard line rhetoric as the Republicans, but they have also played into the hands of the so-called "Miami mafia". An article that appeared in The Miami Herald on August 28th, reports that Kerry's campaign has said he supported Helms-Burton in its early stages, but voted against it because he disagreed with some of the final technical aspects. No matter who is on top, the Miami mafia continues to set the guidelines and parameters when it comes to the obsolete and abusive US-Cuba relations.
Bush's recent restrictions on travel and cash assistance amid complaints from some exiles that he had failed to live up to his campaign promises now opens a new door for dissent and may facilitate a new and fresher Democratic stand on the Cuba issue.
The same article goes on to mention that Democrats cite a July poll as proof that Bush's support among Cuban Americans has softened. The poll showed "Bush's support dropping to 66 percent, from his generally stratospheric support that hovers in the 80s."
It is interesting to note that Kerry/Edwards are not favorites of the Miami mainstream media.
The Miami Herald. “Bush: Kerry soft on Cuba. August 28, 2004.