RDRAM only needs to be in pairs when the chipset implements two RDRAM channels. Apart from the i820 chipset, all current Intel chipsets implement 2 RDRAM channels.
CRIMM terminators are supplied with the motherboard. Since all i850 motherboards have 4 RIMM slots, you must have at least 2 RIMMs; 2 CRIMMs are supplied with the board, in order to have all slots filled.