I think that you just need to cover your bases. Do you have somewhere you can house them in an emergency if you need to rehome them? How would you feel if a serama got injured, possibly seriously?
I have always just watched everyone closely with introductions, and this scenario is a little...
So, depending on the temperament it may just be a regular introduction, but since the Indios are so much bigger that may create issues. I thought I heard indios described as calm though, but you need to see how the individuals are like. Worse comes to worse you may just need to house them...