Voltage Drop on long runs of LED Christmas Lights?
Causing a fire hazard


That is decided by the presence of a non-faked UL Listing (with file number).  Listings from other NRTLs such as CSA or ETL are also acceptable.  

Note that most mail order, everything from Alibaba and AliExpress, and almost anything from eBay or Amazon Marketplace (even if shipped with Prime) is abusing a loophole in Customs/safety regs to sneak in entirely dangerous and defective Cheese junk products. The dead giveaway is the "CE" label they stamp on almost everything, almost always faked; as CE is a voluntary mark only meaningful inside the EU. CCC is another popular fake mark. 


  impacting the life of the bulb


It's LED. What will kill the bulb is the driver electronics being cheap; or weather.  Voltage drop won't affect it one way or the other. 


  Causing any other problems 


Personally, I think running a 500' cord as a single run is a mistake. It will be extremely unwieldy to install.  It has a huge surface area for potential damage, i.e. one hit knocks out 500' of cord instead of a 50' section.  The spools I'm seeing actually don't come with plugs; you are meant to cut the cord to shorter lengths to suit your installation, and put on as many plugs as you need.  

So you should be splitting your power feed a fair bit, not least for handling purposes.