I have been spit-splicing the KnitPicks Andean Silk (55% alpaca, 23% silk, 22% merino) and it felts just beautifully. Of course, the silk doesn't felt, so it probably depends on the percentage of feltable wool-ish fiber.
You can take the girl out of New York, but you can't take New York out of the girl.
But the Russian join is probably still a better bet.
"Choose your friends by their character and your socks by their color. Choosing your socks by their character makes no sense, and choosing your friends by their color is unthinkable." http://RoseByAny.BlogSpot.Com
The alpaca will felt with the alpaca. The silk will just be there. The closest I have come to this is 75% alpaca and 25% acrylic. For a spit join it works fine. I would certainly test it if I was considering felting the whole project as it may be uneven.