vietnam operates scub-b which is limited to 300 km and being land based, it does not have the range to cover a majority of the seas
further more the Shaddock missile(product of the 50's) is outdated having a CEP of some 5000m and having a ranged of some 500km it too cannot cover all the scs
just face the facts, other than a USN intervention, there little to no chance of vietnam winning in any SCS scenario, due to the massive disparities in the military forces. the facts being as they are, the vietnamese government is not going to unilaterally start attacking chinese assets, because thats a really dumb idea and would given the PRC all the pretence it needs to lock down the entire sea, while preventing the involvement of the USN. the story would be wildly different of course if the PLAN fired first.
therefore whatever they are building, will get built, there will be complaints but little if any action. Now vietnam could also build on reefs/islands it controls, and it has clearly done so, having occupied the most number of islands in the area out of all the claimants. but its also possible that china will try to intercept the ships, as it did so against the philippines a little while ago.