Back to the OP, your electric hub will have a different 700c rim to the original one. It will be the same diameter but the width may vary a bit. Rims have a range of suitable tyre width.
Is there any advantage in replacing your 35mm with 28mm?
28mm is a fairly sporty size for hybrid bikes and good for longer commutes. Electric bikes are heavier and less able to be bunny-hopped over obstacles, potholes and rough stuff. Most electric bikes come with fatter tyres to absorb this impact.
You can re-use your existing tyre and inner tube and replace it with another size when it wears out.