ummmmmmmmm...yeahhhh,nevermind,i'm not touching that one...
I'll touch it.
The answer to the original question is
NO.
Just because he didn't play his rookie season or maybe even his upcoming second season doesn't mean his career with the Dolphins is in jeopardy. As benelli1979 mentioned, Rodgers didn't start his first game until his FOURTH year. Most people have Henne taking over sometime during his second year, or most likely at the start of his third year.
Pennington played like a Pro Bowl player this year, and is by far the best QB Miami has had since Dan Marino. Pennington will be 33 at the start of next year, and despite QBs like Kurt Warner and Brett Favre playing late into their 30s, I don't see the same happening for him.
When the Dolphins drafted Henne, they did so with the thought of him being the long term answer. They signed Josh McCown to be the veteran who would hold the job until Henne was ready. It just so happens that things changed, and that veteran turned out not to be McCown, but Pennington.
Having Henne sit his rookie season and learn behind such a great QB mind like Pennington is the best thing that could have happened. It gives Henne some time to get completely adjusted to the game and get more comfortable. Instead of throwing Henne in during his rookie season and struggling, when he does start his first game, he may not look like a first time starter.
Pennington will be the starter at the start of the 09' season, but Henne, who has three years left on his contract, remains the long term answer.