Finishing chicken thighs under broiler
Sure you can broil, however consider this:  Sous vide cooking does not render any of the fat.  So a quick broil might char the outside of the skin, but the fat could remain more rubbery. Some of this will depend on the nature of your chicken thighs.  I've noticed that, depending on the chicken (organic v. non...brand to brand), some chicken is more fatty than others.  One way to deal with this would be to do a good pre-sear, before you sous vide.  Then cook sous vide.  Then post-sear (or broil).