Has there been any indication of using side mounted machine guns like the US Army uses?
The ability is shown on Z-18 mainly , not yet seen on Z-20 , though I am sure it has mounting points.
Personally I doubt we will see a side mounted machine guns like us in PLA army aviation service any time soon.
The whole point of the side mounted machine guns is provide support where attack helicopter support is not available , which under the way US operates , very likely ,Since a lot of small force infiltration happens where you just don't want to 5 helicopter formation , and since helicopter use is common to a point mundane, the Apaches availability are stretched thin.
PLA use helicopter in a much more limited manner , mainly because a Chinese combine army has fewer helicopters then what a US division will have , and doctrinally it is meant mainly to be used with air assault unit . This means it will almost always has Z10 escort ,which is gonna pack a bigger , faster , more deadly punch that any minigun you can put in a Z20.
Though a Z20 mounted with machine guns will likely to happen for the PLA navy , since it doesn't have Z10 attached to it usually , and we might see a fully armed Z20 with rocket pods for the Army as a added firepower used with the Z10s when heavier resistance are expected.