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The net topology would be the same but the actual net names would of course be different as CAM350 has no idea what your CAD netnames would be. The CAM350 netlist also has different header and comment info than the CAD netlist.
What I do is tell CAM350 to "extract" a netlist from the imported Gerber/NC drill files, then import the PADS IPC-D-356 netlist. This method overwrites the netname generated by CAM350 with the CAD netnames. You can then export a "smarter" IPC-D-356, 356A... netlist from CAM350. Some people use the CAM350 link in PADS, and then export ODB++ for even more smarts.
IPC-D-356 is a standardized netlist format. It is not a Gerber format. It contains information about the test points and net connections on a board. It was intended to provide a standard set of information for bare board testing. You can find the table of contents for the standard at:http://www.ipc.org/TOC/IPC-D-356B.pdf
ODB++ is a board fabrication data set developed by Valor. It contains everything about the board - the cad data, netlist, fabrication data, etc. Unfortunately, Valor hasn't done a very good job of sharing the data format completely with the rest of the world. The result is that often times an ODB++ file produced by a PCB program can't be properly read by other CAM or CAD software. Valor has a free reader that can display a board that was saved as ODB++, but you can't use the display for anything except viewing. It also has trouble reading a file if there is even the slightest difference from the Valor "standard". You can see more about the format by going to http://www.valor.com/ , then select "Solutions", "ODB++ Data Exchange".
Don't believe all the hype on that page about how great the format is supposed to be - as I said above, the format has a lot of inconsistency from vendor to vendor.
Of the two file types you asked about, ODB++ is the only one that contains enough information to completely reconstruct the PCB. IPC-D-356 won't tell you anything about the trace widths, component orientations, special board features, etc. - it is strictly for testing net connectivity.