Yes, possibly. But once a flaw has been found in the snap sandbox/container, then it's simply a matter of time and effort to find a snap package with a heartbleed-type hole, then exploit the snap flaw, and bam, you're in. Snap/Docker/et.al. will all have to be gone over with a fine tooth comb to find any flaws.
I haven't looked into it yet, but is the Snap/Docker container maintainer (say that 3 times fast) still responsible for dependency updates, or is there a mechanism to update them automatically, separate from the main app in said container?