I think Pearl did indeed use stock footage from TTT. IIRC, They took advantage of the fact Richard Anderson had also appeared in the feature film. Whether it was unused footage I have no idea.
This might be getting a bit obscure, but FX footage from Space: 1999 was sold by a company specializing in library/stock footage, and the occasional shot not used in any episode was offered. These ended up in other tv shows, films, and even music videos.
http://catacombs.space1999.net/main/images/sfx/sfx.html
Universal infamously pimped out Battlestar Galactica FX footage. The low budget film Space Mutiny as seen on MST3K is a good example, but I’m not sure if any unused footage actually appears.