But possibly not, to use enough C02 in a confined space like a narrowboat bilge may be regrettable. 'The boat didn't blow up, but the workman died' is not the desired outcome.
I do not think that using a vacuum cleaner is advisable. Some cleaners use the filtered air from the cleaner to cool the motor where there may be brushes and sparks. Passing flammable vapour through such an area would be inviting trouble.
The main problem with sparks is with petrol, it has a flashpoint below ambient temperature.
Diesel has a much higher flash point (62°C) and it's auto ignition temperature is about 260°C IIRC so it will ignite at or above that temp, I would not use a grinding disc.
Filling with water untill you have opened up the enclosed spaces is a good idea even if you are using a reciprocating saw. Solid CO2 is an excellent source of an inert atmosphere, if you can get hold of some.