In the Diablo I, II, and III video games, the character can create a town portal to come back to town and sell the loot they have aquired, rest, heal up, etc.
I know, at least I think I do, that the inability for monsters to use the town portal is never addressed in the game, and thus this question should not be about the games.
Is it addressed in any of the novelizations or other extended universe media? Are the denizens of hell able to do so in the novels?
The only portals mentioned in the various Diablo books I've read are demonic portals, not town portals (yet to read the Diablo III fiction). In fact Town Portal usage seems to be limited to the game.
If you're looking for a canon answer we can only extrapolate from the games themselves - since the monsters don't go through Town Portals in the game, we have to assume that if someone used such a spell in the fiction they wouldn't be able to go through.
In multiplayer in Diablo 2, access is party members only. Preventing those hostile to the caster from using the portal.
An argument can be made for extrapolating from there that the portals can only be used by those allied with, or allowed by, the caster, in either case preventing monster access.
The lore indicates that these gates (or the practice to create the gates) were created by the Horadrim
The Horadrim constructed numerous magical gateways between the mighty fortresses so that they could quickly concentrate their defenses against any incursion by the Demons. With but a thought, the Crusaders of the Light could transport themselves to predetermined destinations many leagues apart. Although the secret of creating these gateways has been long lost, it is still possible to use the pathways that are already in place. A Portal opened by means of this spell will always take the caster to the location of the nearest gate and remain open long enough to bring the caster back to his point of origin. The Church of Tristram is built upon the remains of a Horadrim monastery, and it is quite probable that a gateway lies nearby.
The Horadrim were dedicated to removing the demons from Sanctuary, to the point where they led the hunt to capture and seal the Prime Evils. There is no hard evidence to say that a demon cannot use these portals, but due to their prowess in magic, and their dedication to eradicating the demon incursion, it is very likely that they were created with the protection against demon usage.
