Do the operations practices of low-cost airlines represent an increased safety risk?
We should not make statements about any particular airline. Air travel is and remains very safe, due to:


Good practices imposed by the regulatory institutions.
Feedback of things that went wrong in the past to prevent them from happening in the future.
Very mature engineering and technology implementation
Lots and lots of experience with reliability numbers over the decades.


That being said, proper procedures do need to be followed and it could theoretically be the case that only minimal maintenance is carried out at some airlines, while others are more pro-active and lead the field in safety practices. Think Rainman, and the airline that has never crashed.

Safety numbers of all airlines in the developed world are very good. Cheaper airlines must follow the same practices as more expensive airlines. The cheaper tickets are the result of better business practices, not of worse maintenance practices.



Edit

@Michael Kjörling points out a TV episode about a case of Madrid airport being closed, all traffic lining up for Valencia, and three RyanAir aircraft declare fuel emergency. Plus a LAN Chile declares engine out Mayday.

Don't know if this counts as evidence though, TV programs must find or produce a topic that is sensational enough for transmission. The safety numbers are still on RyanAirs side, their safety record is pretty good.