using yeast cake in carboy after blowoff.

So I have a fermenter full of amber ale that is winding down its fermentation and I hear people brewing a batch and just pouring the new beer on the yeast cake. Can this be done with a carboy that had a blowoff?

I mean I can't see though the top because of trub.

If I can't use the dirty carboy, can I pour the yeast cake into another sanitized carboy, although at that point I guess I could just harvest the yeast and instead of diving the washed yeast into small mason jars, just pitch the large volume of "clean" slurry.

Yes you can pour in a clean carboy or boil a mason jar to sanitize and put it in there and put in the icebox, but beware it will build a bit of pressure you will have to relieve unless its fully attenuated....That mason jar lid will buckle trust me:cross:.
I only save the yeast if the beer taste really good but thats just me. Yeast cakes Work great for a Imperial stout, Barley wine, any thing say 1.070 or above. Good Luck!