Trying to test the doSuppressiveFire and was frustrated why the 5 Qilins minigun i set up weren't suppressing the target. Changed the Qilin to another vehicle and low and behold the gunners start shooting at the target.
Did some more testing and the Kamysh also does no suppression. However to my surprise 2S9 Sochor does suppress although you need some distance. And the Qilin AT also suppresses. Don't really know the usefulness of the last one.

The ones i tested that worked: ifrit hmg and gmg, marid, t-100 and t-140k angera although this ones commander also starts suppressing when not told to do so.

I don't know how suppressive fire is calculated. According to the wiki there is a formula but i don't know what that is. I don't know if this is a config issue or an ai issue.