Hi @chemsedine,
not sure what you like to achieve through the Sequencer. There is no direct connection between the Nebula Plugin and the Sequencer.
Basically in V2, you can Create Nebulas as Static-Textures in PIE (like in a seperate Level) and save these to disk, so you can use these outside of Play.
In the upcoming V3 the Nebula-Creation process will be possible in Editor and in PIE, but still not sure how the Sequencer works in tandem.