1) Is Hexagon ready for DIM?
2) Does it work well with DAZ3D 4.6 if I want to exchange files?
No, Hex is not DIM ready and there is really no reason for it to be - although I wish it was because I need to re-download and the resume download function in DIM is really handy for the many interrupted downloads I get from Daz.
Hex is purely a modelling app, so there is no reason for it to exchange files with Studio - there is a bridge between Hex and Studio with that you can consider Hex to be a modelling extension of Studio. Also, both handle the .universal obj format.
Is Carrara a better modelling tool than Hexagon?
Depends n your definition of "better" :)
They both have a reasonably full range of tools and functions - what you do with them depends on your skill and knowledge of them. I and many others prefer Hex for its ease and simplicity, but that could be because of personal preference and familiarity.
Hex is inclined to be pretty quirky and unforgiving of user error, whilst Carrara is pretty much rock-solid.
Hex has the Studio bridge, making it a lot easier to create morphs and content. So, basically, it comes down to want you need the applications for.