The only thing I can find in NJ law prohibiting recaps is this. I think some cop did your friend wrong
Section 13:20-50A.25 - Tires and rims
(a) Tires and rims of proper size and tires with a load-rating commensurate with the chassis manufacturer's GVWR shall be provided.
(b) Tubeless tires mounted on one-piece drop center rims may be used.
(c) All tires shall be of the same size, type, construction, and load-rating. The load-rating shall meet or exceed the GVWR, as required by FMVSS No. 120 (49 CFR § 571.120), incorporated herein by reference, as amended and supplemented. Tires on Type B, C, and D school buses may be of more than one type of construction provided all tires on the same axle are the same type of construction.
(d) A school bus may be equipped with a spare tire and rim assembly of the same size as those mounted on the school bus. A spare tire shall not be stored inside the passenger compartment of the school bus.
(e) A school bus may be equipped with a spare tire carrier properly mounted under the floor in an area accessible to the driver.
(f) The tire tread depth shall at no time be less than 4/32 of an inch on the front tires and 2/32 of an inch on the rear tires as measured on two adjacent treads by a Dill gauge or its equivalent.
(g) Regrooved or recapped tires shall not be used on the front axle of a school bus.
(h) Dual rear tires shall be provided on Type B, C, and D school buses.
(i) Tire chains, snow tires, all-weather tires, or tires marked with "M & S" shall be used for the drive wheels to enhance the safe operation of the school bus during adverse weather conditions. The "M & S" marking is not necessary if a rear tire has a retread that is a snow/mud-type tread and meets the minimum tire tread depth standards of (f) above.
(j) Spacers shall be as specified by the manufacturer and shall not be altered.
N.J. Admin. Code § 13:20-50A.25
And here
N.J. Admin. Code § 16:53-3.25 - Tires and wheels
State Regulations
Compare
(a) An autobus shall be equipped with tires and wheels of sufficient size and construction, as recommended by the manufacturer to meet the GVWR of the autobus.
(b) An autobus shall not be operated with regrooved, retread, or recapped tires on the front wheels. An autobus shall not be operated on any tire having exposed fabric on the tread or sidewall.
(c) An autobus shall not be operated unless the front tires have a tread groove of at least 4/32 of an inch when measured in a major tread groove.
(d) An autobus shall not be operated unless the rear tires have a tread groove of at least 2/32 of an inch when measured in a major tread groove.
(e) An autobus shall be equipped with tires that are matched in size designation, construction, and profile on the same axle. Radial tires shall not be mixed with other types of tires on the same axle.
(f) All autobuses shall meet the requirements set forth in 49 CFR § 393.75, incorporated herein by reference, as amended and supplemented.