I haven't fished for salmon/steelhead yet (with a fly rod), so I can only answer your question in regards to trout, and yes, these types of egg patterns are used for trout, or at least I've used them.
Back in the day, when I first started fishing the Ferry here in northern AZ, I fished something commonly called, "bacon and eggs," which was essentially a SJ worm and an egg pattern on a long double nymph-style rig. Being a tinker, I naturally played around with my options with both patterns, and did for a time use estaz egg patterns. I personally found that they worked best in lower light/murkier water conditions, or even just deeper water conditions. Sometimes they did work for me in high light/clear/shallow water, but I felt they didn't perform as well as a standard yarn pattern under those conditions. YMMV.
I probably have a few of those eggs left, and if I went back to the Ferry when it was overcast, or after a 'flood' discharge, or if they were running a high water flow, I'd probably give one or two a try.
I do have plans to eventually do some steelhead/salmon fishing someday, so maybe I'll tie a few more of those things though.
Peace.