Theoretically, yes. But the degree to which the fluid increases temperature depends on deltaP and flow, flow friction loss. And heat transfer to or from ambient conditions.
sure, it might increase theoretically, but problably not a problem.
However with cylinder in series connection there is usually a built in "leekage" valve in one or both end of stroke positions.
which helps with the syncronisation, therefore the oil between the cylinders also gets exchanged periodically.
if you just take two regular cylinders and connect them in series you might run into issues with syncronisation.
