With the oil consumption of the RX8, think it is safe to use oil additives such as Prolong. I emailed prolong and got this response:

This question has gone back and forth but I was told by race car engine rebuilders that they use prolong when they start up a new engine. It does not hurt the new engine.

I am not sure that this addressed my original question of it being safe in the rotary and if it contains any synthetic additives.
I could use any feedback available. Thanks

The oil that is recommended for the engine already has an additive package that was well thought-out and is the product of over 100 years of research and observations with internal-combustion engines. Don't mess with it.