Yes, a good portion of the heroin would be hydrolyzed to morphine in stomach acid, and also by various enzymes in the liver and blood, but the 3-phenolic ester would be preferentially hydrolyzed (as it's harder to make a phenolic ester than an ester with a 2° alcohol) creating a certain amount of 6-monoacetylmorphine.
There would be an equilibrium reached where a certain portion of the heroin would be present as 6-MAM for some time, instead of total conversion to morphine, depending on the gastric pH and metabolic status of the individual.
6-MAM is more lipophilic than morphine per se and thus would find its way into the CNS more readily.
So, bottom line, you might see a slightly increased potency of oral heroin over oral morphine, but not by much.
As someone else has noted, there were some oral heroin products available and in use back in the "good ol' days." Bayer's "sedative of choice for coughs" was Glyco-Heroin (not sure what the "glyco" part in the name was about - probably just to make it sound fancy).
LOVE ME SOME HEROIN!