Flashforge Dreamer not able to read Cura created G-code file I'm using a second hand Flashforge Dreamer with ABS filament and Cura as slicer.

The Flashforge Dreamer cannot read the printing (G-code) file Cura creates, I think due to not knowing what the printer firmware is? I want to use some of the Cura features that the FlashPrint software does not have. 

What firmware does Flashforge Dreamer use? I think I have to input to cura the machine details (name not listed on list of printers in the drop down menu) and even Google could not tell me, nor the Flashforge website.

Cura has a built-in list of printer specs, but no Flashforge, so even the name of a clone type of the Flashforge using the same type of firmware would help.
For the Flashforge Creator model an alternative firmware is available; Sailfish. However, Sailfish is not available for the Flashforge Dreamer. As a matter of fact, no alternative firmware is available for the Dreamer as a consequence of the Flashforge Dreamer being closed hardware and closed source. 

Not knowing the flavor af firmware (as it is closed source and could well be using a custom firmware build) using Cura to slice models for G-code files gives no guarantee for successful printing.

To be able to use Cura you would have to switch the current board from the Flashforge Dreamer and replace it with a board that accepts Marlin Firmware. Note that there is no default configuration for this pronter available so this requires a little work from you to go through the Marlin configuration file and adjust various constants to make your printer work. [edit: As pointed out below in the comments, in the process you will lose some of the maximum speed the Dreamer is capable of!]

Another option is to buy a license of e.g. Simplify3D (note that I have no affiliation with Simplfy3D!) as they claim to support this printer. There could be other software suites that support your printer.