I do use vudho for healing because I prefer it, but I can tell you that it is certainly not required by any stretch of the imagination.
We had one of our top dps (who uses the default ui) respec to heals for giggles one raid, and he did fine clicking raid frames and pressing keys to heal.
For reference, we are an aotc guild. Yes, the content was on farm and he didn’t top the meters, but he parsed above 50 which is more than acceptable for heroic nyalotha.
The thing about is this: clicking a raid frame and then pressing a button to heal literally doubles ones actions needed in order to throughput healing when compared to using a click-only addon. While this seems strictly worse (which it is) it doesn’t actually matter because at no point is one’s Gcd so fast that requiring twice as many actions will have any affect on performance.
Is it a good idea to get a healing addon and use it if you want to? Of course. Is it mandatory? No. Will a healer who uses an addon outperform someone who doesn’t just by using the addon? No.
I am confident that I could parse just as well using no addons as I can with vudho, even if I could go back in time to 8.3 when I had 80% haste on my rdruid. I use it because it is convienent, thats it.
Dunno if I am logged onto my druid, but for reference I was a 91.6 percentile resto druid prior to prepatch (its a little wonky now).