I do not know in regards to the first shots of Frax in his Workshop-like area however I can tell you that the shots of him following the opening credits is indeed Sentai footage.
After Frax grabs the X-Vault Canister, it then cuts into new footage of the various civilians.
Once you see the white baseball then that is when it goes to Sentai footage.
However it then cuts into new footage of the Silver Guardian SUV.
This shot of the shrouded or rather hooded Venomark is when it goes to Sentai footage.
The footage that plays on Ransik's screen is too hard to determine whether it's new or Sentai.
The Cyclobots as seen in Ransik's flashback, that footage of them is also new.
Here's Ransik and Venomark
Here's another new shot of Venomark
After Ransik teleports away, it then cuts into Sentai footage of the city as well as when it goes back into the Sentai footage for Venomark.
Venomark's file that shows up on the Clock Tower Holoscreen is a Sentai file.
The following footage of Venomark is new until Eric's morph sequence ends. Once it ends, it then cuts to Sentai footage of Venomark.
These shots   is when it goes back to new footage.
Venomark rips off his DNA patch in new footage however it then cuts to a Sentai close-up shot of his DNA.
This shot is when it's new footage.
Here's new footage of Giant Venomark
The shots of Red calling Circuit for the zords is also new.
Once you see the zords coming down the runaway then that is when it goes back to Sentai footage.

Footage comes from Time Episode 39