According to an update
on the Baka-Updates page for Highschool of the Dead x Triage x Lightning Pop
artbook, Yen Press has licensed it.
Correction, the aforementioned artbook is being culminated into the second HotD omnibus.
@to_aru_Oni The Lightning Pop art book will be reproduced in its entirety in the second HSOD omnibus edition.
This would perhaps explain why the date for the second color omnibus of HotD was pushed back until October 29, rather than July 30.