Has anyone tested making an infusion with the closed split mold?

I would like to make a tube of complex geometry and the difficulty is the union of the two parts.

Yes - it can be done well enough and if you can design your tooling to let you infuse through the split line on one side through the laminate to the other then you may not need any consumables besides the bag.  I have done this a few times with MDF and urethane board molds that had resin channels machined into the flanges and the flow distance was short enough that is worked well.  Feed and vac features (spiral wrap?) under that porous teflon peel ply would help too.  Might take a little experimentation but it will (probably) work.  Tube bag is your friend for the inside bag - sealant tape seams down in a tube is no fun.  For unidirectional-heavy laminates like some structural tubes it is nice to infuse across the bundles of uni to help avoid dry zones that the resin skips over because the uni packs too tight.  Agree with Hanaldo that bigger is easier up to a point - then it just becomes a normal infusion but in a hole.  Also agree with Hanaldo that prepreg is the best option for this... but you have to buy into the whole 'I do prepreg' thing or its just too much hassle and expense to justify.