As in all things, it is good to be well-versed in Catholic doctrines when reading or listening to other religious materials. We should be able to differentiate whether what is written or sung is in accordance to Catholic teaching or not, and then to take it from there.
That having said, many of the lyrics of the songs may contain general Christian themes which also hold true to our belief. These you can use even to help you in prayers and meditation if you like.
Not all non- Catholic song writers write songs with heretic themes or lyrics. Some of them have found their way to be used in the liturgy as they are accepted by some local Bishops in their dioceses.
Songs are strong tool for prayers, meditation and spiritual exercise when used wisely and correctly. So I would say, by all means use them but be sure to be clear in your own belief and be able to differentiate what is not.
God bless.