As I stated, BeOS and Haiku are not Linux compatible except on a limited source code basis. I did a quick search for both QT and WxWidgets on BeBits and Haikuware (two places where many people fetch BeOS/Haiku software) and only found a QT from 2001 (2.3.0) on either site. There's no GNOME, KDE, or even X compatibility in either BeOS or Haiku by default, although I have seen an X server running on BeOS many years ago.
If you put enough energy into it, you can make just about anything run on any operating system, but the question is: is it worth it?
That said, yes, someone could port Linux/Unix software over to Haiku relatively easily, especially if they're willing to use native code for GUI, but that doesn't make Haiku a flavor of Linux any more than it makes Windows a flavor of Linux. There are more similarities between a Linux and Haiku binary than a Windows binary, but the fact is that they'd have to be extremely similar for a Linux binary to run on Haiku, and one of the primary goals of Haiku was to maintain binary compatibility with BeOS R5 instead of Linux.
There... I'm done rambling... :-)