I’ve found TNT to be a safe release group, but I haven’t had much experience with cmacked.com. If it is unaltered from TNT’s original release, I would presume it to be safe.
Software cracks often register as malware. I think it is a combination of an attempt at copyright protection, plus the fact that many cracks are essentially breaking, blocking, or spoofing the registration of the software to allow an illegitimate version to run. Just because it says it thinks it is malware doesn’t actually mean that it will do anything malicious to your system that you didn’t already intend for the pirated software.
If you’re super nervous about it, install it in a VM and see what happens.