You have got your self into pretty challenging stuff. I have faced similar kind of challenge in my past with Nx100 controller and in house built servo driven rotation table. They were slave of SLC 500 AB PLC for Mig welding and powder painting.
In my experience you will need to come up with very accurate handshaking algorithm. That algorithm will run by your PLC and direct your robot and rotation table independently to perform tasks.
Try to avoid scenario of your robot painting objects and and your table is rotating same time.
I have done spray and powder painting programming in my past even with 2 years of experience in this I always ask painter how he would paint particular job and try to mimic that human actions into robot. Try to talk to some professional painter and discuss with them that what if you cannot satisfy above quoted condition with available setup how would they paint your job. I am pretty sure they will definitely come up with some good idea.
let me know how it goes.
Although I have to do this challenge anyway, but Your words encouraged me to do it effectively.
To let you more curious, the Motor of the external axis is not manufactured from Yaskawa. But as I tried with all the different ways to get that connection and no one was successful, I was informed by Motoman, that it is not possible to connect a different motor to the Yaskawa controller as long as the Motor does not belong to the Yaskawa company.
So i will change the Motor first of all and then I'll enjoy it