At last it seems like someone at Group Lotus has realised that the best way to get the brand name in the public eye is to go racing. It's why Lotus was formed and in many ways it's what kept them going through some pretty rough times.
To the best of my knowledge, aside from things like the Elise cup which is run at club circuit level this is the first time that Lotus have entered into anything other than F1 since the Esprit's ran as a works outfit at Le Man in 1996.
The last time Lotus tried to run in Indy was in the mid 80's with the Type 96 however the project never got off the ground. There were rumours of the Indy establishement not wanting a full works team in the sport when everyone else was using customer cars and there was a rule introduced before the car raced that banned fully composite chassis so the car would have had to have a redesign before entereing the series, but it's far more likely to be the lack of sposorship that killed it off.