Hi Polly, as far as I know (which admittedly isn't much), they were not, other than by marriage through the daughter Jane Rolfe whose husband was Lieut. Thomas Rolfe
https://www.jstor.org/stable/1920064
https://www.jstor.org/stable/1920064?origin=crossref&seq=2
"The Poythress Family" by William B. Hall
The William and Mary Quarterly
Vol. 15, No. 1 (Jan., 1935), pp. 45-72 (28 pages)
Published by: Omohundro Institute of Early American History and Culture
https://www.jstor.org/stable/1920064?origin=crossref&seq=3
Correction: It's on page 3 (not 2, as linked above).