Based on my experienced, just used this PS3 as what they meant to be, BD for BD player, and DVD for DVD player. PS3 either dual mode lens still using the same lens when they die you need to replace it.
Blu Ray lens are likely vulnerable to heat, i can say they have less life hours than a DVD lens.
PS3 are meant for games once you load the games the lens is not continously working unlike BD or DVD playback.
Anyway, you can use it. However, you are risking the life expectancy of the lens. They should last until the new generation comes out right? IMHO