Dangers in using parallel or series resistors for buck feedback divider
Using multiple standard value resistors in the way you suggest (to stay away from hard to find parts or for BoM proliferation reduction) is a very common practice.

Unless you are trying to get the best possible predicted reliability (as found in MIL-HDBK-217) there really is no practical downside providing you have space on the PCB (although if you cannot fit a couple of extra 0402 parts, things must be really tight).

Note that MIL-HDBK-217 reliability predictions are really a numbers game, so minimising components maximises reliability, all other things being equal.

Note that if you replace a 300k, 1% part with two 150k, 1% parts, you still yield 300k, 1%