Decided to start a new character on normal as haven’t played for sometime. Just before I got to the Whightmare riftgate I encountered 4 rifthound heroes all together!!! Now I was only level 10 and 4 seemed a bit extreme, I just ran around in a big loop to avoid them until I made it to the Whightmare riftgate. Was I just very unlucky with the RNG or are there now 4 hero rifthounds there permanently?
I think it is just luck, I’ve ran into a pack of four rifthound heroes at around level 10 a couple of times in that area.
I notice them more now but it’s great. more loot starting off really helps and a little bit of kiting at early levels makes them easy.
Yeah those guys been around forever regardless of which difficulty you’re on, they seem to have a few different (set?) spawn locations but I don’t think the group spawns 100% of the time and I’m not sure if the locations are specific or I just RNG run into them at the same spots a few times. Fun fight at low levels 
i just ran into those guys on a hc ultimate play through, glad i was able to kite them and get away
It is probably just RNG and it isn’t just the rift hounds… I used to farm Salazar in the Deprived sanctuary a ton (mostly on Ultimate). It wasn’t until I started a summoner and was going through for the first time in normal/veteran that 4 heroes (1 harbinger and 3 voidfiends) spawned in the jaw cells at the front. All lv 25+ when I was lv 18… Only time I’ve been killed playing him so far… Just one of those random things!
I also started a new characters in 1.0.0.4. It seems that the difficulty in Veteran has increased somewhat. There are more hero spawns and more chances to get the “special” spawns. A good change, I think.
In increasing difficulty, there are packs of 4 heroes of rift hounds, tainted hounds, and wind raptors. I met the wind raptors in the Burrwitch outskirts - never seen them in Act 1 before. All good fights. Also I got 3 heroes in the Burrwitch riftgate (like it used to be) where recently I have been getting only 1.
On normal (i.e., not veteran)? It’s not completely unheard of but you definitely got really really unlucky.
If you’re on veteran that’s much more of a regular thing.