Yes, the hub is identical
Same 5x108 PCD and same 63.4 mm centre bore: wheels from Volvo EX40 axe arrière bolt on and centre on Smart #3 without rings. You still need to check the offset and tyres, detailed below.
≈: width estimated from the original tyre size.
Wheel by wheel: offset and tyres
Each original wheel from Volvo EX40 axe arrière is compared with the one from Smart #3 of the same diameter: how much closer the wheel gets to the shock absorber or how far it sticks out of the wheel arch, and whether the tyre keeps the same overall diameter.
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8.5Jx19 ET56 · 255/45R19 — Check on the car
Compared with the original ≈7.5Jx19 ET48 on Smart #3: shock absorber side +20.7 mm, wheel arch side +4.7 mm, tyre diameter +2.6 % : fit it with the original tyre size of Smart #3 (235/45R19), not that of Volvo EX40 axe arrière.
Comparison for guidance only (estimated width). Check in detail
Before fitting the wheels
An identical hub is not enough: offset, width and diameter change the position of the wheel, and larger calipers can touch a smaller wheel. Original wheels often use bolts or nuts with a specific seat: keep the fixings intended for the wheel, with the thread of Smart #3 (M14x1.50), tightened to the torque shown on its vehicle page. Finally, check that the size is among the approved fitments for your vehicle. This comparison is for guidance only: have the fitting approved by a professional.
And the other way round: wheels from Smart #3 on Volvo EX40 axe arrière?