If you want to upgrade, but you worry about just Dolphin, it's most possible that you can go ahead.
If you want a quick answer, it's that Dolphin runs fine in El Capitan (at least for me!). Just yesterday I upgraded from Yosemite to El Capitan and tested Dolphin to see how it performs on my Macbook Pro Retina 13'' late 2013, using the new OS.
