Is a usb adapter a usb modem?

RS-232 serial ports are far slower than USB ports. With very few exceptions, devices that use USB ports would be impractical to use on a serial port.

In short, yes you can, but some devices require more power than others to function properly so you may see a drop in performance or range but yes, the device SHOULD function to a reasonable extent...

The only parallel to USB adapter I've seen is one which allows you to hook up a parallel printer to a USB port on the computer. You could not use that manner to create USB ports.

You should not have any problems doing that. Just make sure that they are compatible.

Acts just like a modem that you would plug into a PCI slot but it's external and portable and you can simply plug it into a USB slot onto your computer.