With crypts, you are going to separate the roots and probably get 2 for 1 before you plant. Usually the way you get crypts is in a little teeny plastic pot with that wool wrap around the roots. When you take that off, you see a tangled mass of roots. (Although I have seen one online source for plants that removes all the leaves before shipping because they say all crypts will melt upon replanting. I say BS to that - I've have two pots of wendtiis in my 20 long that never melted. I'd never buy from them because I'd have to wait for new growth to see if I got what I ordered.)
It will depend on size and weight of rocks, but I think it can be done, especially if you have a crypt that will get some height on it when mature and you locate it around a place where you have driftwood or rocks already. You'd really need to think it through before planting to make sure you can uncover a place as needed for root tabs. And bury those suckers deep, because they can cloud the water if you don't.
A FTS of your tank would help...