The short answer is: It depends entirely on whether your vSAN traffic ever leaves those Top-of-Rack (ToR) switches.
The golden rule of Jumbo Frames (MTU 9000) is that they must be configured end-to-end on every single device in the data path. If even one switch or port in the path has a lower MTU, the packets will be dropped or fragmented, which will cause severe vSAN performance issues or cluster partitions.
Here is how to determine if your core switch needs the change:
Scenario 1: You ONLY need to change the ToR Switch
You do not need to change the MTU on the core switch if:
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All your vSAN hosts are plugged into the exact same ToR switch (or the same pair of stacked/VLT ToR switches).
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The vSAN VLAN is completely isolated to the ToR switches and does not traverse uplinks to the Core switch.
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Your vSAN traffic is strictly Layer 2 (no routing between different vSAN subnets).
In this scenario, the vSAN traffic flows from Host A $\rightarrow$ ToR Switch $\rightarrow$ Host B. Because the core switch is never touched by this traffic, its MTU setting doesn't matter for vSAN.
Scenario 2: You MUST change the Core Switch
You must configure MTU 9000 on the core switch if:
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Your vSAN cluster spans multiple racks, meaning traffic has to go from ToR A $\rightarrow$ Core $\rightarrow$ ToR B.
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You are using a vSAN Stretched Cluster across different physical rooms or sites.
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You are routing vSAN traffic over Layer 3, and the gateway/router lives on the Core switch.
Don't Forget the vSphere Side!
Changing the physical switches is only half the battle. To actually use Jumbo Frames, you must also set the MTU to 9000 in VMware: