Would if be okay to have knee replacement surgery with venous disease?

Mostly yes: It depends on the severity of the venous disease and the presence/absence of other comorbidities but most of the time knee replacement surgery is safe.

Treat veins forst: Often it is advisable to treat underlying venous disease before knee surgery. This often makes the knee surgery easier by reducing abnormal venous pressure. This can reduce bleeding and also the chance of blood clots in the abnormal veins.