It really shouldn't be a problem if the fork seals are even remotely servicable. The difference in pressure between the inside and outside of the fork at altitude is nothing compared to the forces exerted on it while bottoming it out on a sharp impact.

What type of plane does not have pressure controled baggage areas? Some kind of small business jet? All the commercial aircraft I've worked on have all had pressurized baggage bays.

One more thought - your oil filled fork might be considered hazardous materials. It might be a good idea to check it out.