Yes, the hub is identical
Same 5x108 PCD and same 63.4 mm centre bore: wheels from Smart #1 bolt on and centre on Volvo EX30 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 Smart #1 is compared with the one from Volvo EX30 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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≈7.5Jx18 ET50 · 235/50R18 — Check on the car
Compared with the original 7.5Jx18 ET46 on Volvo EX30: shock absorber side +4 mm, wheel arch side −4 mm, tyre diameter −1.8 %.
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 Volvo EX30 (-), 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 Volvo EX30 on Smart #1?