I don’t have any direct knowledge or evidence, but to me, it would just be plain EVIL to not handle SIGINT.
Hm. Actually, I can offer some assurance: strings /sbin/fsck | grep sig reports:
sigaction
Warning... %s for device %s exited with signal %d.
So I’ll just take this as anectdotal evidence that the fsck developers are calling sigaction to handle the relevant signals.