While their respective abilities allow them to walk or move while in midair, the methods in executing the moves are entirely different.
Guy's Eight Gates removes limiters on the body and the user is temporarily granted approximately a hundred times their normal power, far beyond that of the five Kage. Unlocking all gates, however, results to a user's death afterwards. Guy only did not die because Naruto helped him. Because of his immense power, he was able to kick the air successively until he reached Madara.
Sanji's Skywalk, on the other hand, is similar is executed by kicking the air to jump higher, giving the appearance of flight. It has no known risks, however, unlike Guy's Eight Gates. It is also not mentioned if it requires removing a body's limiters like Guy's.
So, while the techniques might sound the same, they're still different. Below is a list of significant differences:
- Requires the Eight Inner Gates formation so it's only possible when executing another technique
- Is not used by other shinobi, or was not shown in the manga to be used by others as far as I know so it is unique to Guy's Eight Gates
- The user will have to be in the final stage of the Eight Inner Gates in order to demonstrate this ability, resulting to the user's death afterwards
- Has no specifics or prerequisites at all so it is a technique that can be performed on its own
- Does not need successive kicks to be able to stay afloat in midair, as shown here
- Used by others so it is not unique to Sanji
- Has no known risks mentioned or specified, nor any physical strain shown or emphasized
There is a technique in Naruto called Walking on Air Technique, which collects water under the feet while continuously releasing chakra to walk in the air. This is, however, from Fanon Canon Rebirth and from what I understand, is not written by Masashi Kishimoto.
Regarding each other's influences, I don't think they drew inspiration from each other's works, or at least it wasn't mentioned. They seem to, however, draw influence both from Akira Toriyama's Dragon Ball. (Source 1, Source 2)
To conclude, it would not be impossible if both characters would have similar techniques since they make use of their legs during their fights. However, the Skywalk technique demonstrated by both are entirely different from each other, especially in terms of how it benefits the user itself.