Do you mean security in terms of safety on the job? Or do you mean job security in terms of being able to count on having the position for a long time?
Regarding safety, I think hostel work is pretty safe. Aside from some cleaning chemicals the job doesn’t involve working with hazardous materials, and it rarely involves physically dangerous activities. We’re constantly surrounded by people too, so if something goes wrong we usually have someone there to back us up even when we’re working alone on a shift.
Regarding a stable position, hostels tend to have quite high staff turnover. There are a number of factors that cause this, but not least of all:
The kind of dynamic people who are great at hostel work are also great at many other things, and therefore in high demand (and risk of being lured away)
Listening to travelers share their stories all day tends to incite a deep sense of itchy feet and a need for hostel workers to go traveling themselves
Burnout among hostel staff is common because it takes so much energy and passion to be a great host
Hostels frequently offers salaries that are lower than other jobs could offer due to the nature of the business
If someone is working hard and enjoying the hostel, then most hostel managers are likely to want to keep them for as long as they can.
Seasonal hostels offer less job security because they close down for significant periods each year and therefore can’t provide work.
Hopefully at least some of this answers your question. :)