The odds that a nuclear weapon was used in combat in Yemen and it didn't make the mainstream news are so remote as to be laughable. This video is likely just a large conventional explosive misinterpreted as nuclear by people who think that "mushroom cloud" must mean "nuclear."
Another sign that this is BS is the fact that "bunker buster" and "neutron bomb" make no sense together. A neutron bomb is designed to decrease the explosive force while increasing the amount of radiation produced, with the idea that tank crews are easier to kill through radiation (which tank hulls don't protect against very well) than through blast (which tank hulls are great at protecting against). But radiation is a bad weapon against underground targets, where each foot of soil acts as shielding to reduce the amount of radiation by a factor of something like three. To destroy bunkers, you want blast, not radiation.
A mushroom cloud is an artifact of air convection produced by any sufficiently large blast. Peculiar to nuclear weapons is a bright initial flash of light (actually two flashes, but they're close enough together to be very hard to distinguish by eye). If this video depicted a nuclear initiation, such a flash would appear around 0:15, but none does.
https://www.youtube.com/watch?v=OTE_Eshm2xw
(I say supposedly as the only articles about this as on conspiracy-theory sites, but it looks pretty realistic)