From
https://en.wikipedia.org/wiki/Clive_Cussler:
"Kurt Austin, Joe Zavala and Dirk Pitt all make cameo appearances in the fourth book in the series, Skeleton Coast; Juan speaks to Pitt on the telephone, and Austin and Zavala appear at the end."
NUMA Files adventure novels(co-authored with Paul Kemprecos on the first eight, Graham Brown on the rest)
'This series of books focuses on Kurt Austin, Team Leader of NUMA's Special Assignments division and his adventures. Some characters from the Pitt novels appear such as Sandecker, Rudi Gunn, Hiram Yaeger and St. Julien Perlmutter. Pitt makes brief appearances in the books "Serpent", "White Death", "Polar Shift", and "Devil's Gate."'
I have not read these, and it is not indicated whether or not these characters directly interact.
