Yes it is, well its buffered ascorbic acid and calcium citrate is buffered citric acid and calcium malate is buffered malic acid. So they dont need to be taken with the drink .
I suppose you could mix them with it but I would wait until you can purchase the calcium hydoxide other wise your ACV measurements may be off.
There are many types of calciums and dont beleive I would recommend any of them replace C.hydoxide in the drink.
I would try not to mess with a good thing ! MLs drink has great testimony and I dont beleive any of them are from someone who has'nt used the C.Hydroxide and many not until they increased the dosage.