Is ECC memory fine for real-time audio work?

Yes, you will not notice the performance hit from ECC memory in real-time audio work. The overhead is only 1-2% in memory bandwidth, and audio production rarely saturates that — your bottleneck is usually the CPU. What you will notice is the stability: ECC catches memory errors that cause pops, clicks, or crashes, while non-ECC lets them through. If you can get ECC support, do it.