Yes they can.
1. You have to understand that in those days, most of the monitor uses VGA input.
2. That means as long as your graphics card have a VGA output(there should be a converter in the box too), you can output the signal out to the monitor
3. You can visualise it as:
Your old television set have spoilt, so you bought a new LCD tv. As long as the new tv supports the antenna input, you can use it to watch programs. Just that now, your antenna jack is spoilt, as long as you change it into someting that your tv supports, you can use it.
Note: Older monitors like CRT cannot support HD resolution, meaning to say you wont see very clear pictures compared to LCD monitors.
But also due to the lower resolution, the graphics card will not have to use so much power to produce the same speed of gameplay when compared to producing the same amount of speed at higher resolution on the LCD monitor.