Yes and No. Comparing their influence to rock n roll is not the same. While many of Robert Johnson's songs were covered by people in Britain like Cream, Rolling Stones, etc, the style of music is completely different. Robert Johnson's songs were constructed still a little differently. You have to understand the "fad" in the 50's and early 60's in Britain after everyone got through with their Skiffle fads...they got a hold of American blues records from guys like Robert Johnson and put their own spin on it that a few other guys like Louis Jordan and Stick McGhee had kind of been doing.
If you're going to say that Robert Johnson invented rock and roll, then you better give credit to every other Mississippi Delta blues player at the time because the only reason Robert Johnson's songs were covered is because kids in britain in the late 50s and early 60s got a hold of his records and liked what they heard, and decided to put their own spin on it. Robert Johnson didn't invent rock and roll, he just influenced certain facets of it.
Anyway, if you listen to Louis Jordan, who is considered the top or one of the top Jump Blues guys, it sounds a lot like Rock n Roll except it's from the 40s, not 1951-1956.
If you were to play the song Saturday Night Fish Fry by Louis Jordan (which is considered to a lot as the first Rock N' Roll record by the way) to someone who isn't 100% up on their 20th century music history, I can almost guarantee you they'd think it was an early rock and roll (R&B) song from the 50's even though it's from 1948/1949. You could go back even further to say 1946 and Choo Choo Ch'Boogie which sounds like an early rock song.
Do a little research on Louis Jordan's producer Milt Gabler from the 40's, who produced all of Bill Haley's hits and Jordan's guitarist who was a major influence on guys like Chuck Berry.
YouTube - Louis Jordan - Saturday Night Fish Fry