Yes, the recently launched Moto C supports USB OTG support and I am really happy with its performance as I recently bought this phone but you have to connect it through the OTG cable or Pendrive and here is the link for OTG cables and OTG Pendrives.
Check complete specs of the phone here: Moto C specs
Both the phones have their pros and cons, I think you should go for Redmi 4A, Redmi 4A has the following advantages over Moto C.
1.Redmi 4A faster CPU than Motorola Moto C. Faster CPU means more smooth experience.
2.Redmi 4A has more RAM than Motorola Moto C. More RAM means more applications can run at the same time,
3.It has better screen more pixels than Motorola Moto C. More resolution means sharper and crisper screen.
4. It is slimmer and lighter than Motorola Moto C. Slimmer devices are easier to carry in pocket and look more fashionable.
5.It has battery Capacity than Motorola Moto C.
It is not like that it is a one sided game, Moto C has the following advantages -
1.It has has Front Camera Flash ,having a front camera flash allows you to take selfies in low light.
2.It has Removable Battery.It has replace the battery or use a spare battery when device's battery performance is degraded.
Verdict - In my opinion, Redmi 4A is better overall performance and price ,if you need front camera and removable battery than go for Moto C.
You can also compare these devices on 91mobilesMoto C vs Xiaomi Redmi 4A
Check the video