You can use this strategy for regular polygons with an internal angle greater than $120$ (that is, with $7$ or more sides): use $n$ equilateral triangles of side length $1$ to cover each side of the polygon, so that the uncovered region also forms an equilateral polygon of side length $1$.
Here's an example for a regular heptagon:

The importance of the internal angle greater than $120$ is, of course, so that the equilateral triangles don't overlap at the corner.
If your regular polygon have $3$, $4$ or $6$ sides, the situation is easy to handle. If it have $5$ sides, a similar strategy will work, so the answer to your question is: yes, it's always possible.