|Young joshua tree in desert landscape|
A. I tried to think of reasons why this person would tell you this and I cannot think of any.
I don't agree. These are very good choices close to a pool area. What is nice about plants such as these is that you can direct their root system with the location of your water supply. I suppose there could be cracks in the pool that would allow for leaks. However, most plants go after water which is the cleanest. If you apply drip irrigation to the sides of the plants away from the pool this will encourage their roots to grow in this direction.
Water them with shallow irrigations, perhaps no more than a foot deep and don't do it very often. In Midsummer if you want to encourage growth water them every two to four weeks. If you want them to slow down, water them less often. Watch carefully for agave weevil attacking and killing primarily agaves and in particular American agave. I have posted information on their control in this blog. You can search for it by entering agave weevil in the search box.