A Greensting Scorpion is a vermin with 1 HD, and it is mindless (INT —). The monster creation rules don't allow a mindless creature to get the usual extra feat that all other creatures with 1 HD do. But if this scorpion becomes a familiar and it loses its mindless status, it will have at least INT 6. Does it gain its previously-negated feat slot?
It retains the appearance, Hit Dice, base attack bonus, base save bonuses, skills, and feats of the normal animal it once was [...]
and further down,
Use the basic statistics for a creature of the familiar's kind, but with the following changes.
Hit Dice: [...]
Hit Points: [...]
Saving Throws: [...]
Note no mention of feats there.
There is a box below labelled FYI: Feats for Animal Companions & Familiars. Clicking through to any of the listed feat descriptions gives you the following info:
Special: Feats that are meant for familiars can be switched out for a familiar's default feats (as listed in the familiar's statistics) if the familiar meets the prerequisites. Such feat replacements must be made when the PC first acquires a new familiar, and like all new feats from supplemental sources the new feats should be approved by the GM before being integrated into play.
So, if a familiar's base creature type has feats, these may be swapped out (with GM permission), but they do not gain more.
In the specific case of the Greensting Scorpion you mention, it has one feat: Weapon Finesse. So, with GM permission, you may be able to swap it out.