Not really. Pigpen was more of a blues singer, and New Riders did mostly country songs. New Riders did start off as a Dead spinoff band, but it was Jerry, Phil and Mickey. The bands toured together in 1969-70. New Riders would play their set, then dead would do an acoustic set, then their eclectic set. By later in 1970 when New Riders released Power Glide they replaced Jerry with Buddy Cage. Jerry still did shows with them once in a while.
From wiki wiki:
In addition to Nelson, Dawson (on
acoustic guitar), and Garcia (continuing to play pedal steel), the original line-up of the band that came to be known as the New Riders of the Purple Sage (a nod to the
Foy Willing-led
Western swing combo from the 1940s,
Riders of the Purple Sage, which borrowed its name from the
Zane Grey novel) consisted of
Alembic Studio engineer Bob Matthews on electric bass and
Mickey Hart of the Grateful Dead; bassist
Phil Lesh also played sporadically with the ensemble in lieu of Matthews through the end of the year, as documented by the late 1969 demos later included on the
Before Time Began archival release. Lyricist
Robert Hunter briefly rehearsed with the band on bass in early 1970 before the permanent hiring of Torbert in April of that year.
[7] The most commercially successful configuration of the New Riders would come to encompass Dawson, Nelson, Torbert,
Spencer Dryden, and
Buddy Cage.
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