The shutoffs on your first pic look exactly like the one on my micromatic single. I thought it was a check valve. Maybe I should go check...
B
I've got the same ones on my Micromatic Nitrogen Regulator...if you go to the replacement parts...and link to the Shutoff valve...there is no mention of it having a check valve inside. I've never taken mine off to look. Check valves have a little spring that holds a ball against the barb end of the valve. Like was said...it's only there to prevent the contents of your keg from backing up into your regulator....most likely in the case of the keg tipping over or running out of gas in your CO2/N2 tank -- with the added benefit of keeping your beer from going flat should your tank run empty. I've had plenty of setups that don't even have the check valve and it's not been a problem.
You could probably take a pipe cleaner and insert it in the end of the barb with the valve opened (of course make sure you don't have the regulator connected to anything)...if the pipe cleaner hits something before the valve knob...it's probably that little ball valve. If it's free to go past the valve knob...then you certainly don't have a check valve in there.
IF you have a tube attached to the short diptube in your keg...going to a airstone in the bottom of the tank for carbonating/nitrogenating...THEN you'd better have the check valve b/c you could easily get a back flow of liquid if the pressure were to raise in the keg (temp, secondary fermentation, etc..) Otherwise, liquid more than likely won't be backing up anyway, ...except if you were to cause foaming in the tank by jostling it around, getting it warm, infections, releasing the pressure rapidly, etc.... or tipping the tank on it's side. I just make sure I disconnect the gas connector before I store a keg in a cooler on it's side for transport.
If you do allow stuff to back up in your gas line...it will probably get infected at some point and taint every other keg you connect it to, until you get it cleaned out and disinfected.
If you buy a used Sankey coupler...you might check to see if the rubber check vavle is inside the coupler. It may have been used to daisy chain kegs...in which case they remove the check valve from every coupler except for the one that's actually connected to the gas supply. This way they can run 2 or more kegs to a single tap without having to stop the party to tap another keg.
High Volume Draught Beer Systems Using Series Keg - Facts and Techniques