Seems like PHP 7 is not crashing on simple stuff anymore (the 5 bugs mentioned above were resolved). After removing debug symbols, it would appear the blogs were true, that PHP 7 is around 50% faster than 5.6.
Will continue to keep an eye out, but for now PHP 7 is deployed here. The live environment should allow for more thorough testing of PHP 7 and VaultWiki's compatibility with it.
Note that vBulletin 4 and lower are not compatible with PHP 7 out-of-the-box, due to:
https://wiki.php.net/rfc/uniform_variable_syntax
You must be comfortable with hacking vBulletin a bit and modifying core files if you intend to use PHP 7 with it. Although the changes would be minor (using braces {} to fix ambiguous lines of code), it is unlikely that vBulletin 4 will ever be officially updated with PHP 7 support.
So far it would appear no changes are necessary in VaultWiki itself, but we have made various optimizations and refactors anyway to make a number of marginal performance gains.