Uguisudani is fine -- it's a residential neighborhood; it feels a bit seedy at night but I think that's because its reputation precedes it.
Permit me to cut through the coy innuendo. There's a lot of prostitution going on in Uguisudani. The love hotels around there aren't a symptom of a sketchy reputation. They're there to serve an industry that rents rooms by the hour.
The more seedy stuff happens a bit further to the east and north.
I guess you're talking about the Senzoku red light district, which is walking distance from Uguisudani. There might be more prostitution happening there. It's an area that has traditionally housed many brothels. It's also a "residential neighbourhood". Is prostitution in brothels more seedy than prostitution in hotel rooms? That's a subjective view, I think.
Many of the low-rent hotels and backpacker hostels are located in this corner of Tokyo. For hundreds of years, these have been the "poorer quarters where the ragged people go". Some of the backpacker hostels are converted from old "takoya" which previously housed day laborers. Today they offer the cheapest possible "tourist" accommodations in somewhat unsalubrious but perfectly safe neighborhoods.