Could GaAs reflective-open SPDT be used as RF signal spliter?
Could I use reflictive-open GaAs SPDT and apply equal ON-voltage to control pins (V1 and V2 at picture)

No you can't, look in the schematic at how the transistors are connected, if you make the pass transistors (Q1 and Q2) conductive (which is what you want) you will at the same time also make Q3 and Q4 conductive which will short the signal to ground.

You can solve this by using 2 SPDT switches from which you only use on switch. You then ground the other contact of the switch.

But a GaAs SPDT is generally only used in RF applications and in RF applications you don't just split a signal like that because you will not have a 50 ohms (or whatever value) characteristic impedance anymore.

So if this is for RF, you must use a proper splitter. If you don't your signal will be deformed/distorted/reflected/etc. Real RF engineers will point and laugh at you so don't ! Use a proper splitter !