Is it true that dummy turboactivate.dll is able to bypass activation?
No. Do a simple hash check or verify the Authenticode signature of the dll and you stop this particular "dummy dll" crack. And if you're using C/C++/Objectve-C then just use the static version of TurboActivate.
If you're trying to stop all cracks, then let me be the person to break it to you: there is absolutely no way to stop cracking of software. Some shady licensing companies will lie to you and say they have the "secret sauce" that can stop cracking. But those are just lies.
From "What is hardware-locked licensing and why choose LimeLM?":
What is software licensing?
Software licensing allows you to get paid for each copy of your software. The types of software licensing come in a few general forms which I'll be covering in the next section. With few exceptions the hardware-locked licensing is best for businesses because it allows you to have absolute control over where your software is installed.
The point of licensing isn't to stop crackers from cracking your software. The point of licensing is to increase your revenue by preventing casual piracy (using serials over and over again). There is real money to be made by stopping casual piracy.