I don't believe it.
In between his bouts of meglomania Gore has shown sign of political sense. For a guy like him to get elected from a red state like Tennesee is one sign of this and latching onto Bill Clinton is another.
What he did to the country after the 2000 election shows he will calculate - he played that just long enough to get him a lifetime martyr appointment but no so long as to get blamed for paralyzing the government.
He can see what happened to Leiberman who went from lukewarm Democratic support to almost none after he ran independent.
Instead...
1. Floating this balloon keeps Ralph Nader out of the race.
2. Forces Democratic candidates to focus on global warming to prevent his entry.
3. Gives him the opportunity to form an exploratory committee, if he wants to, to collect donations and run ads.
Net Effects:
1. Neutral to Hillary - keeps Nader out but forces Democrats to the left to guard their liberal flank - shouldn't generate too much animosity.
2. Positive Gore's ego.