I think your setup is probably really good - what I would do is minimise the inconveniences.
You might already be doing this, but maybe you could set up a Reason template with all the outputs from redrum going straight to the hardware interface as a slave. Save this template and always start from there. Maybe you could do the same with Live? You probably already do this, but there you go.
Ultrabeat has been changed for new Logic, but my experience of it from Logic 7 was that it was interesting, but a totally steep learning curve. IMHO, the interface is a mess, and makes no sense - it's supposed to be a semi-modular synth, but it seems overcomplicated to me. It will take a while to get used to Ultrabeat. I discovered Ultrabeat before I started using Reason, and I just didn't use it at all, it seems confusing. I confess to not reading the manual properly, but even so, I didn't read the manual for Redrum, because it's intuitive. Ultrabeat to me seems counter-intuitive, very uncharacteristic for an Apple product.
You might like it, but make sure you try it out, as it could be an expensive mistake. Apple does have an equivalent of elastic audio, it's called AppleLoops - it's a little fiddly, but it is good.
What you have to think about is the time and frustation that you might sacrifice in the short-term for the long-term frustration that you've been experiencing already. I think the best thing you can do is try Ultrabeat out somewhere - go to an Apple store. It could be the answer, or it could be a bigger headache.