You'll likely get a lot of opinions. I'll give you the "no opinion included" version. The bottom line is - no matter what opinions you receive, you will not know unless you try it yourself.
If every sound you want to use will sound great through a pair of 2x12 recto cabs, the powered head will give you a sound and feel like a real guitar amp. It can be miced onstage, or a line can be sent to the PA (the line to the PA would include Kemper cabinets)
If you want to use sounds that would compromised through recto cabs, then consider powered full range cabinets (OR - use a powered head with passive monitors). The trade off is, you will be listening to the amp/cab and microphone sound onstage. The feel is more like really loud studio monitors - a subtle difference to some, a big difference to some.
Can you get him to bring his Kemper to your house/borrow it from him?
That way, you can turn it up, and see for yourself 
But, you will get more versatility with Atomic cabs than Recto cabs.
Yep, a very linear active cab (or a linear power amp + a linear passive cab) will let you hear each profiles the closest to how they have been created.
It's not that a guitar cab will sound less "tubey": it will just sound different than the original profile, because a guitar cab imparts a strong character to any sound.
You might kill the cab portion of the profiles by pushing a button, and use your cab(s): your result will be as you were playing many different amps through the same cab: you'll like some a lot, some others not at all... but you will always be able to tweak them.
OTOH, buying a passive Profiler and an aftermarket power amp will make you save some money (in some cases lots of money).
Note: the above is only true for the Lunchbox format, not for the rack format:)
A final note: if you buy a(ny) linear power amp, you'll be able to go the guitar cab route or the linear passive cab one.
HTH
