I wanted to convert gerber files to ODB++ to use them in simulation software and see if the modification done by the PCB vendor are OK or not. The conversion is done successfully and the generated ODB++ can be view by other ODB++ viewers (Valor) but it can not be opened by simulation software. It seems since the netlist information is not present in the gerber, it is also not existing in ODB++ as well. I was hoping that the tool would somehow detect the nets and name them.
Yes, you can use FAB 3000 to add Netlist information, plus any other necessary ODB++ properties/attributes that your simulation software may require. My first suggestion would be during ODB++ Export to check the option "Optimize for Third-party software) - see below.
Here's another somewhat related link, https://support.numericalinnovations.com/support/discussions/topics/14000018124