In the past, there have been numerous crossovers of Indy champ car drivers competing in the Daytona 500 and other assorted support races.
In fact, two Indy 500 winners have also been Daytona 500 victors — Mario Andretti in a Holman-Moody prepared Ford (1967) and A.J. Foyt in a Wood Brothers Mercury (1972).
Three-time Indy winner Johnny Rutherford notched a victory in his introduction to NASCAR at Daytona — a 1963 triumph in one of the 100-mile qualifying races. Other Indy winners who have appeared with NASCAR include Parnelli Jones, Tom Sneva, Gordon Johncock, the Unser brothers, Rodger Ward, Troy Ruttman and Al Unser, Jr.
The year Mario won, other so-called crossovers in the race included Gary Bettenhausen, A.J. Foyt, Jim Hurtubise and Johncock. Among other Indy veterans running with NASCAR on occasion, have been the likes of Jerry Grant, Dan Gurney, Jim McElreath and Dick Rathmann. Rathmann scored 13 wins when NASCAR was running shows on dirt.
However, this year’s Daytona 500 will see the unprecedented participation of four former Indy 500 winners — Dario Franchitti, Sam Hornish, Jr., Juan Pablo Montoya and Jacques Villeneuve.
The flood gate certainly has opened, demonstrating a reversal of roles — Daytona (and NASCAR) displacing the Indy Racing League competitors as the reigning major sanctioning body. The prestigious Indy 500 will continue to draw crowds, yet, it appears to now be the stepping stone to NASCAR.
With Indy’s legendary and historical past, NASCAR’s first title champ, Robert “Red” Byron (1916-1960) was at the Speedway in 1947 and 1948 using a V-8 flathead Ford. Even with the aid of ace racing mechanic Red Vogt, he still failed to make the race. 
Several other NASCAR standouts came North in the 1950s. Marshall Teague and Frank Mundy come to mind. Teague left NASCAR as his relationship with the organization soured. He not only ran stock cars up North, but saw duty as a champ car driver, appearing in a pair of Indy shows and finishing seventh in 1957.
One of the earlier drivers defies the general pattern of a short stint with NASCAR or champ cars before returning to his roots. Paul Goldsmith moved back and forth competing with both sanctioning bodies. He notched nine wins with the stockers and in his Indy career he had a third-place finish in 1960.
In 1963, Junior Johnson, the winner of the second Daytona 500 in 1960, was at Indy as he attempted to place a Kurtis Offy in the 500 field.
Wanting at least a partial roof, Junior had a roll cage on the Kurtis, yet, he did not attempt to qualify.
A strong turnabout came in 1970, when A.J. Foyt had NASCAR veteran Donnie Allison in one of his cars.
Allison went the distance, finishing a respectable fourth and garnering rookie of the year honors. The following year, Allison finished sixth. Yet, unbelievably, no solid offers followed. Lee Roy Yarbrough, another NASCAR hotshot was on the Indy scene a year prior to Donnie, finishing 23rd. He was back to compete again in 1970 and ran 19th.
Cale Yarborough, who went on to win three NASCAR championships, ran Indianapolis four consecutive years, culminating with a 10th-place finish in 1972.
Bobby Allison was coaxed into an Indy car for the 1973 Hoosier Classic by Roger Penske. He was back in 1975 in a Penske car that again experienced a mechanical problem to finish 25th. Allison went on to win three Daytona 500s. 
As for the King, Richard Petty, he made it perfectly clear during his annual STP sponsored visit to IMS on the opening day of qualification that he harbored zero interest in getting into one of the jet-like Indy racers.