I would suppose so, but due to both Knuckles' and Shadow's independent natures, it would be more fitting to call them "allies".
Chat with our AI personalities
So many i have lost count. depends if you count shadow and knuckles as sonic's friends
Shadow
The answer is Knuckles the Enchilada, but she likes Shadow the most because she is always with him. She had a crush on Knuckles but since he wasn't paying attention to her, she is now in love with Shadow. Rouge used to have a crush on Knuckles, but now it is said that she likes both knuckles AND Shadow. P.s. Shadow does not like Amy or Takil. Rouge the bat loves Knuckles, and Knuckles loves Rouge back. In the one episode of Sonic, Knuckles is blushing when Rouge is next to him.
Shadow and Knuckles are both the strongest Sonic characters.
Because SEGA officialy accepted relationship between Knuckles and Rouge.