High Power UV led array for SLA printer
Is my conclusion correct?


No. It is very unlikely that the current will be evenly divided between the two strings. I have found with white high power LEDs the mismatch in current typically exceeds 20% 

I rad some tests on three Bridglux EB Gen 2 strips wired in parallel.  Bridgelux uses "binned" LEDs so the strips Vf are fairly close. I measured each strip individually at 500 mA.     





The above strips used binned LED.  I made some strips using 16 Luxeon Rebel white LEDs from the same reel. You can expect results similar to 40-60% mismatch like this:   





I would recommend using a Texas Instruments 
LM3466 Multi-String LED Current Balancer for Use with Constant-Current Power Supplies 





 


  Would the LED's be able to sustain the additional 50ma above their
  rated current? 
  
  Would this lead to a shortened lifespan or just kill the LED outright?


Most high power LED have a "test current" at which they are spec'd. The maximum current is usually higher than the test current. 

I doubt an additional 7% current would damage the LEDs. What is more important is that the temperature of the LEDs do not get too hot.  


  I want to connect them to a 50W constant current power supply at
  1500ma, I want to connect them 2 parallel series of 8 LEDs.


Eight 3.5V LEDs would need a 30V CC driver.  I would recommend a Mean Well HLG 60H-36A with a current adjustment range of 1000 - 1700 mA or a HLG 60H-36B where the max current can be set with a resistor.