Are there endoscopic technologies for blood vessels?
Blood is hard to see through, so visualization with a camera isn't used (to my knowledge). However, Intravascular ultrasound can be used, though it is expensive and not all that common. Instead, angiography is usually used, by filling the vessels with a radio-opaque dye

There are also many techniques used to treat vascular conditions, like balloons/stents to open and keep open blocked or partially blocked vessels, or to repair valves. You can read more about Interventional cardiology or minimally invasive procedures.