I guess it depends on how much risk you consider the vasculitis to be. In our case my wife is bipolar. We don't declare it, and don't expect to be covered for it, or it's consequences, as the costs are based on the worst possible example and expectation (which can be suicide). But then it's been over 20 years since she had a psychotic episode, and takes her meds conscientiously, so we don't expect there to be any problems related to it. I know insurers can be "creative" in refusing payouts, but I guess we'll just take the risk.
Pedalcover are a brokers, so if you have an issue with them, you're unlikely to find a cost effective alternative - though you may be able to get cover at a price if insuring direct with an underwriter.