Do they? I wasnt aware that Axis got any damage reduction vs satchel charges... Though 20% reduction doesnt actually stop a satchel charge oneshotting infantry most of the time, except closing in at max range, since they have 240 damage base (Soviet ones apparently do 340 for whatever reason)
If you don't trust me, go test yourself.
FYI, here is my test. After throwing shatchel, I ran into the kubel. Only cavalry rifle got 4 units killed.
While Axis had no units killed. (All auto-attack has been disabled by cheat mode)
+ Another test with allied unit as enemy confirmed that they do gets killed. So... I'm not sure the exact mechanism over satchel dmg over inf, but it is clear that it deals more than 80 to any allies inf. while it deals maximum of 68(according to the Korean stat site) to the Axis inf units.
+ Calvary satchel & Soviet satchel shares same data. It's default dmg is 340, but vehicle gets 70% dmg(240) and I guess infs. also get somewhat damage reduction to 80. And Axis inf gets + 20% dmg reduction(68).
CoH2 stats are so complicated yet their is no way to know for exactly unless someone decompile the game itself. I whish this thing gets updated in CoH3. For example, ST2 has in-game unit stat wiki.