Per Lumpkin request.
This photo is from the San Diego Union of January 14, 1969, right after the Padres signed Thompson following a massive tryout of prospects. The accompanying article said that 18-year-old pitcher Thompson was to report to the Padres' spring training camp in Yuma in February for spring training, but my assumption is that he would arrive in the minor league section of that camp. He was destined for Class A Key West all along. I found no indication that he was a non-roster invitee to the major league camp.
Marvin Thompson Minor Leagues Statistics & History | Baseball-Reference.com
Regarding Lumpkin's remaining requests, I don't have photos of them and they don't appear to be non-roster invitees nor spring roster players. 1) I think Jim Allen is Pitcher James Richard Allen, who lived in San Diego, but whose baseball-reference record shows no association with the Padres. 2) Terry Gardner was a minor league pitcher from 1967 through 1970, the last two years coming within the Padres' system. 3) Salvador Gonzalez is not listed in baseball-reference.com. I have no idea who he is. I tried spelling the last name as Gonzales, but that didn't help. 4) Robert P. "Bob" O'Brien was a pitcher and outfielder in the Cubs' system in 1969 and Padres' system in 1970.
P.S. I stand corrected. Lumpkin has provided a 1969 Padres spring listing on the major league thread which shows that the above five players were indeed non-roster invitees to the 1969 Padres' spring camp.