He should...however, if he is working on the one in the back that is harder for you to see, he may be doing this for a reason...some fish don't like to be watched and can feel safer and do a better job, so you may want to leave it to help increase you chance for success...now that I think about it......
Fish will often eat their eggs/fry when they feel threatened-as odd as this sounds they would rather get the nutrition than let something else get the nutrition-they do this so that they will have more energy to spawn again in a safer place to improve chance of success.
Oh and... one more question, if you don't mind-
there are two cups in his enclosure. He's working on the side in one and he's working on the middle in the other. Should I keep them both in there or remove one?
Betta slave-I put both my breeders in the tank at the same time-so that neither have established territory-both male and female release hormone and phermone that trigger spawning-the male hormone trigger the female eggs to ripen-the female pheramone tell the male that she is ripe and ready to breed.
I don't rely on the the size of the nest or building of the nest as a sign of readiness-after spawning the male usually will build a proper nest and move the eggs to it after spawning in some cases-also the eggs will float after the male puts them in a bubble
I would go ahead and release both in the spawning tank and see what happens...
Weluvbettas-you still need to make water changes with most soil until they start their submersed life and become water logged. I would hold off on adding any ferts until the plants look to need it-the soil should have enough nutrients along with fish waste to feed the plants...too much plant food and you can end up with algae problems.
What do you mean by "what else can I have in there"