Personally I installed php 7.0 on my server and my WPMU worked without any problem. I use this plugins directly on my WPMU main site:
Admin Ads, Admin Panel Tips, Affiliate, Avatars For Multisite, Blog Activity, Cloner, Comments Control, Content Monitor, Dashboard Feeds, Domain Mapping, HTML Email Templates, Multi-Domains for Multisite, Multisite Theme Manager, New Blog Templates, Pro Sites, Reports, Select Language At Signup, Set Blog Description on Blog Creation, Simple Sitemaps For Multisite, Site Generator Replacement, SmartCrawl, Snapshot, Support System, User Activity, User Reports, WP Defender, WP Hummingbird, WP Smush Pro, WPMU DEV Videos
All of this plugins work fine on my server with php 7.0 and I hasn't any problem with this tile now. Even I tested all of this plugin with HHVM, and all of this worked fine.