Finally I discovered why on some custom ROM (eg: SlimBeam) my dashclock extensions aren't visible!!!
These ROMs includes in bundle a different release of dashclock (else numbered as 1.5) that doesn't includes the new dashclock API (2.0).
DashNet and DashCallLog are compiled including the new dashclock API and this is the reason why they aren't visible on the main widget.........don't ask me the reason of that.....but I compiled the DashNet 1.5.2 with the old API (1.1) and it works like it must.... here the link for this special release:
DashNet for custom ROMs (API 1.1)
DashCallLog will be soon.
Official release are on market and are always recommended if works with your ROM.
DashNet official release (API 2.0)
Many thanks to Giuseppe (Matrix) for the report!!