In short, no! You don't need to be able to read music to learn to play slide guitar (or any instrument, actually!).
Many musicians will tell you that they don't read sheet music, they have learned to play by ear or using guitar tabs. Slide guitar is particularly adaptable for learning when you don't read music, because the whole style is rooted in listening and feeling your way with the guitar, rather than reading the notation. Many of the greatest slide guitar players the world has ever seen do not read music.
Most slide guitar students learn to play using tablature (tabs) or chord charts, or just by watching and listening to the pros. In this way, you learn the finger positions you need without being required to read sheet music.
When you're learning slide, your ears are essential in the process! You can learn to rely on your hearing to let you know when you play a note in tune and when you need to slide into a note smoothly. This is a more useful process to learn than actually reading music.
Slide guitar is rooted in blues and rock, and for these styles, you may not need to read music. However, it is more likely to be helpful if you wish to branch out into jazz or classical music. To learn slide, your most useful tools will be your ears, your practice time and your patience!
To get started with learning slide guitar, give me a shout and we’ll get your free one to one session booked in: https://calendly.com/philliphenrymusic/slide-success-discovery-call