Qustion
Can EventBridge Pipe in account A target Kinesis Firehose in account B?
What does documentation state?
The documentation is very vague about it. It doesn't say it's possible, but neither it states the opposite.
What do I think?
I think it's impossible, since EventBridge (and pipes are a part of it) can't route events to an AWS service in different account. In this case you would need an additional event bus in the account B, route the event from event bus in account A to event bus in account B, and from there - to the destination service.
But, please, prove me wrong
What do you think?
Correct, today EventBridge Pipes cannot directly deliver events across accounts. Workarounds would be using EventBridge Event Buses (as Pipe target) (https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-cross-account.html) or Step Functions (https://aws.amazon.com/blogs/compute/introducing-cross-account-access-capabilities-for-aws-step-functions/) for cross-account routing.