is nukes completely useless?

Infolinks -> Concept -> Nuclear Ordnance

If you detonated them in the middle of their fleet (i.e. not homing), then yes, they are useless. If they were way closer, they could do some damage, maybe even disabling a ship (not too sure about this though, depends on the ship). Another way to use nukes is to shine the enemy nozzles up with them, most likely disabling them (for some reason they will still appear functional in the UI, but if you look at them you'll notice most of them won't work anymore). I'm not sure if this trick can reliably be used in VO (Vesta Overkill) though, since they are 4 ships and it's a lot of area to cover with nukes.

Missiles are good for screening drones.

Also, one of the problems with Devastators is that they are awful even by meagre stock design standards.
They are death sentence to the launching ship if it's intercepted before emptying magazines, have beyond abysmal dV and have neither survivability or even hitting power to make up for this.

The only way to sensibly use them against capship fleets with existing PD is preboosting them with the launching capship.
Still when I did gold VO with stock module custom ships I actually used rough SillySiloship counterparts with 50 Devastators and a lot of other stuff each.

Overall nukes can be pretty effective but they really benefit from being combined with some way to do kinetic damage* (even by just homing for collision, especially with delayed warheads).

*)
Flak and nuke on a single missile is subject to the explosion teleportation AKA "brimstone" bug, mind you,

Yes, you doing it wrong! Nukes in space battle is just the same "missiles" as, for example, flaks. I.e., you should use it in massive swarms! Try to launch 100 nukes+100 flaks, covered with drones, and you'll get the point.