Is it safe to limit current and increase voltage above VF for LED
If your circuit delivers limited current, then the LED itself will 'regulate' the output voltage to whatever Vf it needs at that current and temperature. 

In the datasheet you linked to, the forward voltage at any given current is given as typical. You supply the 700mA, and the LED will clamp that to 18.2V, maybe more, maybe less.

If the supply voltage to your current limiter is well above Vf, then your current limiter needs to be designed to handle the voltage difference across it, when passing the required LED current. 

If it's a linear device, then it needs to be able to handle the heat dissipation.

If it's a switch mode (SMPS) device, then it doesn't need to handle so much heat, but does need the right inductor value and timings to deliver sufficiently constant current at the input voltage you provide.

The data sheet gives a typical forward voltage. It would have been nice if they had also given an absolute maximum, just in case you were designing a buck SMPS, or if not caring about efficiency, a linear regulator. In those two cases, your supply voltage has to be above the highest expected LED Vf. With a boost SMPS, no such problem arises.