Update: You can create Custom Slide Transitions with a Pro plan:https://ajarproductions.com/blog/2018/05/30/create-awesome-slides-from-indesign-using-in5s-presentation-mode/
If you're referring to the SWF transitions in InDesign, they are not used by in5. in5 has its own transition options, known as the Page Format in the in5 dialog.