Tried different configurations, but as a result I have blinking\disappearing crosshair in normal mode and its total absense in zoom mode.
Playing with NV GT 9600

I can confirm this. I have also clipping issues with my crosshair and I have no crosshair while zooming. The clipping issues beginning, when the first mission briefing information (The yellow text in the bottom left corner) appears or if I use the scope.
IMO, it seems to be a zbuffer problem in the rendering of the GUI.
I modified the graphical settings and playing around with the flags in the game.ini, but I did not found a solution.

I have this problem too, someone know how fix this?

dgVoodoo might fix this!
Firstly, search the internet for 'dgVoodoo' and download. Open the zip and copy dgvoodoosetup.exe as well as the three files inside the MS folder (but not the folder itself) into the Outbreak directory (for me: C:\Games\Outbreak). Now, run dgvoodoosetup.exe and click the .\ in the top left corner. Next, go into the DirectX tab. Set resolution to the highest you can choose, and VRAM to your system. Untick dgVoodoo Watermark option
Now it should be fixed!
Optional:
Modern systems should be able to handle this! Set Anti-Aliasing to the highest option you can see.

I hope this helps!