Keeping the profit you can make in mind, i also think the situation is ok. The only thing which can be annoying are these AC trolls, who show up there, from time to time. But this is a general problem and not one for Den in particular.
You can scout the area first with a sneaker on your own to see if there are other sneaks or even players around. Also it's of course no good idea to come there during prime time, at least if you don't have some kind of backup.
I do those slave runs pretty often. Sometimes i DO have some guys in the back but in most cases it's me on my own, fearing the risk of beeing shot by some PKs (as everyone else). But if i successfully finished like 3 out of 5 runs (for example) it totally pays off.
@Jotisz
I agree that slaveruns shouldn't be safe, however I do think it would be nice to have some kind of work at Vortis too maybe a delivery to some Slaver Camp (generated location), though since that would need a new map maybe just a delivery to Den, Raider base and VC. Its just an idea so I haven't worked it out in more details but the reward from this shouldn't be too hight like with slaveruns.
Some kind of additional quest for a small amount of caps as reward there would be nice, yes. By the way, you also still should be able to sell slaves in VC (must be citizen ofc) too. Even though they turn into "servants" after you sold them

.
In general some kind of connection between DEN and VC would be good too. Additionally to the slave runs Metzger could offer some kind of "caravan guard" job. Somewhere the servants for VC must come from and this "somewhere" is most probably the slaver guild. So he would hand out a bunch of slaves and you have to bring them to Vault City in one piece. Since this is just a small delivery quest the reward shouldn't be that high too.