Here's a list I made of the Star Trek actors who appeared in The Twilight Zone.
TOS
William Shatner - "Nick of Time" 1960, "Nightmare at 20,000 Feet" 1963
Leonard Nimoy - "The Quality of Mercy" 1961
James Doohan - "Valley of the Shadow" 1963
George Takei - "The Encounter" 1964
TNG
Jonathan Frakes - "But Can She Type" 1985
Brent Spiner - "Dead Run" 1985
John DeLancie - "Dead Run" 1985
James Cromwell - "A Message From Charity" 1985
DS9
Terry Ferrell - "The After Hours" (remake of the original) 1986
Nana Visitor - "Dead Woman's Shoes" (remake of original "Dead Man's Shoes" ) 1985
Andrew Robinson - "Profile in Silver" 1985, "Private Channel" 1986
Louise Fletcher - "The Hunters" 1988
Jeffrey Combs - "Placebo Effect" 2003
VOYAGER
Robert Duncan McNeil - "A Message From Charity" 1985
Tim Russ - "Kentucky Rye" 1985, "Voices In The Earth" 1986
Ethan Phillips - "Devil's Alphabet" 1985
Gerrit Ghraham (Q / Quinn) - "Welcome to Winfield" 1985
Anthony De Longis ( First Maje Culluh) - "The Convict's Piano" 1986
TOS
William Shatner - "Nick of Time" 1960, "Nightmare at 20,000 Feet" 1963
Leonard Nimoy - "The Quality of Mercy" 1961
James Doohan - "Valley of the Shadow" 1963
George Takei - "The Encounter" 1964
TNG
Jonathan Frakes - "But Can She Type" 1985
Brent Spiner - "Dead Run" 1985
John DeLancie - "Dead Run" 1985
James Cromwell - "A Message From Charity" 1985
DS9
Terry Ferrell - "The After Hours" (remake of the original) 1986
Nana Visitor - "Dead Woman's Shoes" (remake of original "Dead Man's Shoes" ) 1985
Andrew Robinson - "Profile in Silver" 1985, "Private Channel" 1986
Louise Fletcher - "The Hunters" 1988
Jeffrey Combs - "Placebo Effect" 2003
VOYAGER
Robert Duncan McNeil - "A Message From Charity" 1985
Tim Russ - "Kentucky Rye" 1985, "Voices In The Earth" 1986
Ethan Phillips - "Devil's Alphabet" 1985
Gerrit Ghraham (Q / Quinn) - "Welcome to Winfield" 1985
Anthony De Longis ( First Maje Culluh) - "The Convict's Piano" 1986