use DIM from here in a real Daz account?

I always do manual installs, so I couldn't tell you, but if you (are naïve enough to) log into DAZ from DAZ Studio, then I would guess that the answer would be a very firm "no", but only out of general paranoia.

I doubt that DAZ does an inventory of all your stuff and report/sue you for piracy or whatever, but it never hurts to be cautious and use basic privateer hygiene.

Absolutely safe, I've been doing it for years. The software has no ability to contact DAZ and tell them what you are using, and why would it? It was designed to allow you to use assets from other vendors and freebies you made yourself or acquired elsewhere.

Sometimes I've acquired an asset for testing purposes and by the time I decided to buy it, there has been an update. DIM tells me there has been an update and overwrites the previous version, no problem.

I do use some precautions. All assets acquired for testing get saved to a different folder than the ones downloaded from DAZ. Work in off-line mode in DIM when installing these files. When switching between these files and downloads from DAZ, I just need to change the "Package Archive" folder in the Advanced Settings in DIM.