Depth Fade and Fresnel inputs in a Particle's Material will result in the particle not rendering unless Mobile HDR is checked true on an iOS device.
Also Reproduced in Main Promotable-CL-2535351
Specifically tested on iPhone 5s, iOS 7.1.1
Particle Material Setup:
RESULTS: Particles are not drawn at all
EXPECTED: Particles are drawn with Depth Fade
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-15147 in the post.