Yes, you can use one webhook across multiple, branded campaigns (partitions) within Marketo.
If you are managing multiple campaigns for multiple brands (in multiple partitions) in Marketo, you can setup one webhook that all the brands / campaigns can use. To do this, you'll want to use tokens within your webhook template for anything that needs to be brand-specific. Then, simply assign the tokens in your Marketo Programs, the same way you would for emails, landing pages, and smart campaigns. See the Marketo Docs for more details on managing tokens.
However, it may be advisable to use a unique webhook per brand for flexibility. This would allow you to make changes to a brand-specific webhook without impacting any other brands webhook. Ultimately, it depends on the unique requirements of each of your brands and the diversity of the content in your Marketo campaigns.