Yes, 9- or 10-speed cassettes also fit on an 8-speed freehub (you noted this in your post where you said you bought wheels for 8, 9, or 10 speeds). These all use the same freehub body, so you can go up to 10 speeds without frame or wheel modification. 9-speed would require a 9-speed chain and a 9-speed shifter. 10-speed would require a 10-speed chain, a 10-speed shifter, a 10-speed derailleur if you're doing index shifting, and possibly different chain rings (if they don't play nicely with the narrow 10-speed chain). You shouldn't have any problems like that with 9-speed.