No. You shouldn't have any problems. When I was on Windows 8.1, I used a multiboot USB many times and never had an issue. And, in case you still have doubts, I created that bootable drive with YUMI too.
Also, in my own UEFI firmware, I have the option to set my Boot order to CSM but to boot UEFI first if a UEFI system is detected. I always set my UEFI up this way. Whenever I am booting normally from my internal hard drive (which has a UEFI system) it boots in UEFI mode. Whenever I want to boot from the bootable drive I just hit F12 during startup to enter my Boot Options and choose the bootable drive. No need to be dipping in your UEFI settings all the time. BTW, your hot key to get into the Boot Options may be different from mines.
Last of all, I know it may be obvious, but you must turn Secure Boot off.
Edited by Agouti, 08 February 2016 - 10:35 AM.