you will need hub centric spacers for the blazers. (have the center of the spacers missing)

Personally I've been running spacers for about 6 years now. I started out with 1.25" spacers on the rear to even it out with the front axle width. Then when I swapped in the wider ZR2 axle I moved them to the front to even it out with the rear axle. I've never had a problem with them. All that being said, I agree with what Rex, Diaita, and a couple others have said in that if you're buying new rims just go with a set that have lower backspacing. It keeps things simpler and you have less potential points of failure.

If you go the wheel spacer route make sure that they are both hub-centric (have the cutout for the hub lip) as well as being wheel-centric (have the lip to go inside the cutout on the wheel) and get them from a reputable seller. Being hub-centric as well as wheel-centric helps the spacers properly support the weight of the vehicle on the hub rather than the studs.

If you decide to use spacers you must be absolutely sure that you torque the lug nuts to factory specifications on both the spacer and wheels, and you have to pull your wheels off after 100 miles or so and retorque the lug nuts on the spacers. Some people also use locktite to help make sure the spacer lug nuts don't back off.