The DET3 is capable of driving up to 8 injectors directly (up to 4 per output channel). Most customers just use the DET3 to modify the MAF or MAP sensor signal, as you have to start from scratch building a fuel map when using the DET3 in "fuel implant" mode.
If your factory rev limiter is fuel only, then yes, you should be able to raise the rev limit when using the DET3 in fuel implant mode.
There were some old school piggy back systems, I believe HKS was one which had 1-2 injectors placed on the '3000' crossover pipe before the throttle body. Not the most efficient method but it has been done, they are quite rare to find now.
An a more important note the injectors have nothing to do with the rev limit.......................:/
Some factory ECUs impose the rev limit by cutting fuel, not ignition. In that case, driving the injectors from a piggyback would allow you to raise your rev limit. So yes, the signal to the injectors can be related to your rev limit.