No, your optics are not compatible. You need to have the same optics (MM to MM or SM to SM) on both the 6500 and 3750.
SFP-10G-SR is a MMF and it uses a LC duplex connector.
X2-10GB-LRM is also a MMF and it uses LC duplex connector.
so they are compatible.
Under 6xxx series switches you will both transceivers as part of the supported devices.
Under 3xxx series switches:
Link for 10GBASE X2 modules:
10 transceiver modules compatibility matrix:
Look for Table 1 10-Gigabit Ethernet Transceiver Module Models
both are multimode but the wavelengths are different. the LRM (longrange) runs at 1310nm the other (short range) runs at 850nm. Distances are quite similar depending on what type of MM cable you use. (few hundred metres).
So they are not compatible.