Ventilation is a serious problem. IPE will rot and warp if moisture trapped underneath. Requires adequate airflow to prevent condensation build up. While IPE is otherwise as close to indestructible as any wood can be, it is vulnerable to moisture and is specifically not rated for ground contact for this reason. If you use it on a rooftop deck, you should make sure there is airflow underneath. This may require vents on the house side and opening on the outside end of the deck with support rafters running outward (so air can flow under the boards.) I would also use as wide a board spacing as practical. Use of 5/4 board thickness would would slightly decrease the odds of warp/cupping and allow wider rafter spacing for better airflow. Most important issue is whether you can raise the deck sufficiently to allow adequate airflow underneath. If not, IPE not a good idea. (I do not know about Massaranduba)

I have been looking at Curupay wood decking. What I liked about it was the color. It is light with darker bands/stripes. But when left in the sun it darkens to a maroon with very dark bands color. It is reported to be very hard like Ironwood. I think it might be a lower cost than Ipe.

Anchor seal is a must in my book to keep the ends form checking. I would not glue down the boards as this will not allow the proper expansion and contraction of the wood from my perspective. Grace Vycor on the joists or anything for that matter would not be a good idea either in my mind.

I like the sound of your Contractor far as the clips go,massaranduba/bullet wood is some good material and the money is right with it. Ipe is geting a little spendy for good reason. The normal mill with Mass has some defects,nothing goes thru the planer like ipe, but with the good side up thats no big deal. 1x6 S Americal material with the same install will cup the same as 1x4 you just dont notice it as much. Mass needs to be installed in a timley nature this wood does not like to be left in the sun while the frame is being built x 10 with the biger material like 2x4/4x4. I my own self have a 16 x16' Mass deck to the back of Butler Manor 7 years old the John is real happy with it. Working with Mass required a small learning curve,seems like your Guy has aready been thru that circle. J.