Atuk,
Yes, Aramco allows flying of two types at the same time. Several years ago a Safety Audit recommended that our pilots be allowed to fly more than one type at the same time to help dispel complacency. Currently we have the following aircraft pairings:
Dash-8 F/O - CE-550 F/O
Dash 8 F/O - Hawker 800 F/O
B 737 F/O - AT -802 Captain
Hawker Captain - G-IV F/O
Dash 8 Captain - Twin Otter Captain
CE-550 Captain - AT-802 Captain
B 737 captain - AT-802 Captain
B 737 Captain - Twin Otter Captain
We also have many pilots who fly both left and right seat on the same aircraft type.
Although this list only shows what's currently going on we've had virtually every concievable combination happen, including a very few guys selected for triple positions (usually F/O in all three seats like CE-550, Dash 8, B 737) and senior management guys holdng G-IV Captain - B 737 Captain.
Lately to avoid scheduling problems we've moved away from having people hold positions in two "busy fleets" I.e. no Dash 8 - B 737 combos, however, if you're current in both and needed we do move guys around as required (usually to cover a temporary shortage), pay by the way, is not affected by position filled. You could be paid like a 737 Captain but fly as skipper in the Twin Otter (becaue primarily you are a 737 Captain).
In fact our pay is very different than most airline ops, it's complicated but in short you come in at a pre negotiated salary and it just goes up (and up) each year. Unlike most other airlines we ARE evaluated SUBJECTIVELY based on performance, personal skills, whether you're upgrading eqiupment, extra duties performed (officework, extra aircraft flying, etc.) and other stuff that management deems important. Average increases vary between 4% and 15% per year. Being pilots we always whine about the injustice of our merit increase but in reality very, very few leave because they weren't paid enough for the work performed. Of course theres alot of other variables that go into pay,but I'm really deviating from your question, I just wanted to press home the point that you are typically paid for the highest paying position you perform.
As far as flying multiple types I think it's great, no one is really forced to do it and many actively ask for it (I always have), I consider it a major perk of working fror Aramco; you can bush fly while still making airline wages. If you're tired of airline flying try this for a bit, it's really different, even if you only fly our 737 operation, it's unique.