On my CX bike, I ran an older 105 derailleur (spec'd for a max 27 cog) with an 11-32 cassette. It worked but the clearance was really tight so I went to a mountain bike derailleur. An ultegra derailleur spec'd for 27 works like a dream with a 28 large cog on my road bike.

What I'm saying is that a derailleur that is spec'd for a 30 max cog may work just fine with a 32.