Depends on what you mean by "adult". From my understanding, engineer gobies shouldn't be kept in captivity. As juveniles they're fine, but adults are a different story. In the wild, adults live in a burrow in monogamous pairs with thousands of offspring, constantly maintaining their burrow. During the day, the young venture out to feed. When the juveniles return in the evening, the adults take them into their mouth then spit them out. Analysis of the guts of adults have revealed them to be completely empty, save for some green slime. Furthermore, no adult has been observed to leave their tunnels to feed. This suggests that the adults are either some sort of gods or that they probably feed off bacteria in their tunnels and the slime of their young.
In my opinion (I've never kept this species before, so don't quote me on this), for the physical and psychological well being of the fish, I'd definitely recommend having a nice deep layer of substrate for the big guy to muck around in. And I understand that just because certain behaviours are exhibited in the wild, they don't necessarily need to happen in captivity as well. However, since adults in the wild literally spend the entire day maintaining their tunnels and sucking on their babies, you're going to end up having problems with him if he can't play with some sand. In case you're wondering, I have a certificate in animal behaviour, training, and enrichment.