We were able to get this stuff off, but it took some doing. Scraping turned out to be really slow and ineffective. We ended up pressure washing it first (which was still painfully slow, the nozzle had to be less than an inch from the concrete to be effective). Pressure washing removed most of the bulk but left a lot of residue. Then we used WD40 to dissolve the residue into a goo, and mopped and scrubbed the goo with scrub brushes. Then we pressure washed it again to clear the goo out. After that we resealed it with an epoxy coating to lock in any remaining residues in the pores. (we did the epoxy because after living with the horrible smell for a month, I was paranoid that it would not be fully eliminated)
Dirty, dirty job and took 2 full days for 600sf. ugh.
But at least it is done, and my project is back on track :-)
Thanks for the input!