Are vascular conditions a disease or a symptom of another disease?

Too broad. The question is too broad.Vascular disease could be venous or arterial. Arterial disease is more frequent with certain medical issues, high blood pressure, diabetes, elevated cholesterol and triglyceride, smokers, family history.
A disease. They occasionally can be a symptom of something else but most often they are a disease state themselves.
Vascular disease/PAD. Hard arteries with plaque is atherosclerosis. Other diseases accelerate pad plaque build up; hypertension, hyperlipidemia, diabetes, and nicotine addiction. Heart attack, stroke, limb loss, sudden death are vascular events. Medical therapy for all the diseases is important. Surgical therapies, stent, balloon and bypass when plaques cause symptoms.
Either. There is a an entity called peripheral arterial disease. On the other hand certain other diseases can lead to vascular disease or clogging of blood vessels such as lupus.