Yes, saline solution can be used as eye drops. In fact, most eye drops are contains saline solution(with some preservative added in). You can even make it your own if you have distilled water and salt. If you do it yourself, you must remember that use distilled water because water carries contaminants very well.
Yes. Saline solution can be used as eye drops safely to rewet your eyes. But make sure it is distilled water because water contains contaminants which may cause eye infection. Or you cannot use disinfected solution in which there are some bacteria which would do harm to your eyes. However, saline solution can be used as eye drops if you want to use them to keep your eyes moist. Before you use them, you'd better ask your doctor for advice.