Does the renal vein have a greater glucose concentration than the renal artery?
The kidneys use glucose from the blood as a nutrient, so, this is the reasoning behind your source saying there is less glucose in the renal veins than in the arteries.

If the renal vein contains both less of water and glucose than the renal artery, the concentration of glucose in the renal vein still be lower. This agrees with Bioninja.com.au:


  Blood in the renal vein (i.e. after the kidney) will have:
  
  
  Less urea (large amounts of urea is removed via the nephrons to form urine)
  Less water and solutes / ions (amount removed will depend on the hydration status of the individual)
  Less glucose and oxygen (not eliminated, but used by the kidney to generate energy and fuel metabolic reactions)
  More carbon dioxide (produced by the kidneys as a by-product of metabolic reactions)
  


On the other hand, an article in Scielo.br says:


  Unlike the proximal nephron, cells in the distal nephron are fully
  capable of glucose utilization. In physiologic conditions, the amount
  of glucose utilized in the distal segments of the nephron equals that
  derived from the renal gluconeogenesis in proximal tubules. This is
  confirmed by the common finding that the arterial-renal vein blood
  glucose concentration difference in the post-absorptive state is near
  zero.


In conclusion, your source can still be right.