Israel isn't even recognised as an independent state by several Asian countries; many of them would refuse to play
Israel if their teams, or clubs, were drawn together.
All fifteen former states of the USSR were invited to join UEFA when the Soviet Union broke up in the early 1990s; the invitation still stands, which is why Kazakhstan (which is partly in Europe, but mostly in Asia) is now a member of UEFA. Uzbekhistan may join them in the next few years.
Most of Russia is indeed in Asia, though most of the population live in Europe, west of the Urals. There is
a team currently in the top division in Russia from Vladivostok, which is on the Pacific coast and is further east than a large part of Australia. Currently they are bottom of the Russian Premier League, but if they were to finish high enough there is no reason why they shouldn't play in the UEFA Cup.