Does Master Yi, Wuju Bladesman still give the +2 passive bonus when Switcheroo is played?

Yes — Master Yi's +2 still applies.

Master Yi, Wuju Bladesman ("While a friendly unit defends alone, it gets +2 might") is a passive continuous effect that applies whenever its condition is met; Switcheroo doesn't turn it off. Switcheroo only swaps Might by applying +X/−X modifiers that last until end of turn (Rule 433.1.a), and it calculates the swap from each unit's current Might — including Yi's +2 if it's already active. Any later Might changes, including passives like Yi's, are simply added on top of the swap's modifier (FAQ #8531).

So the defending unit keeps its +2 from Yi both before and after the swap; only its Might number shifts, not the bonus.