For those unaware, Sambo is actually just Judo with a slightly tweaked ruleset. The founder of Sambo was originally a Judoka who learned everything he knew from the Kodokan in Japan. Later, some wrestling techniques were added to Sambo, although Judo always had wrestling techniques itself (its just a form of jacket wrestling which have been around for hundreds of years). The creation of Sambo also had a lot to do with Russia wanting to separate the art from its Japanese roots and make it distinctly "Soviet" at the time.
The reason I mention all that is because most people referred to as Sambo grapplers are really Judoka, or have trained in both. Leg grabs in Judo are set to make a comeback soon too, so the popularity of Judo in the U.S. should grow some more and hopefully attract more talent. But Judo has always been a great style for MMA, it's just needed some tweaks. The main reason you don't see it as often in MMA is because unlike BJJ, most Judoka are trying to make the Olympics. Their goal isn't to go into MMA. There's also a lucrative career after the Olympics if they can do fairly well. With wresting in America, there isn't much after the Olympics, or even college wrestling. That's why you see more American wrestlers in MMA than Judoka. But both are efficient styles for MMA.
Fedor was actually way more of a Judoka than he ever was a wrestler or Samboist. He medaled in the Russian Judo Federation National Championships two years in a row in 1998 and 1999. He didn't really compete until 2002, 2005 and 2007 when he did the Sambo World Championships.
Actually, most Sambo guys in Eastern block countries are just failed Judoka. Judo has the deepest pool of competitors of any martial art in the world with the Olympics and its other competitions. When those guys can't make a country team for Judo, they end up going to sport Sambo or combat Sambo because the talent pool is so much lower.
That's incorrect. That's combat Sambo. Sport Sambo does not involve strikes and is basically Judo but with tweaked rules and clothing.