I don't have an iMac Pro, but I have a 2019 5k iMac with the i9 processor, 1 terabyte SSD, Vega 48 and 40Gb's of RAM, which is basically the same as the base iMac Pro. I also have the iPad Pro 3rd Generation 12.9 inch with the new pencil and the apple smart keyboard. I love this combination and it perfectly suits my needs as a University student. I needed an iPad because I use the pencil a lot for my studies and I use a program which is only available on the iPad, so a MacBook was not suitable for me. However it can also do everything that I need a portable computer to do such as word processing with MS Office. It's also more portable than any MacBook and I like some of the extra features it has such as FaceID and it has much better cameras than the MacBooks. For my needs, the iPad Pro is superior to any MacBook.
I also wanted a powerful home computer when I'm at home studying and so I got the 2019 5k iMac. I saved around $1400 going with this one instead of with the base iMac Pro, so I'm happy to get basically the same performance but for a lot less money. The iMac works great with the iPad Pro, as would most modern Apple computers. I have no troubles with working between either of them. Most of my work is stored in the cloud so I can access the work on both the iMac and the iPad easily. I don't have any troubles with either machine and of course the Apple ecosystem means they work very smoothly together. But I guess this depends on the software you use as well. But I think having an iMac or iMac Pro gives you the best desktop experience and having the iPad Pro gives you the best portable experience if you need the pencil and you don't need specific apps that are only available on desktop when you're out an about with your computer.
Also some of the future features in Catalina such as Sidecar will likely make the iMac and iPad even more useful together and with iPadOS coming, the iPad will be even more useful as a portable computer. I think this combination is a really great combination.
