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Some documentation - like the Haynes manual - implies it. The Volvo documentation is explicit: only the intake valves have the seals on the valvestems.

I did some more digging, even the 16V versions, the B204F and B234F, only have the seals on the inlet valves - albeit a different type, the same as the 850's 5 cylinder engines use.
This one seems to be of a different material (teflon?) and can also be found on the exhaust valves of later Volvo engines.

If you look trough forums, there's no concensus to the usage of seals on the exhaust valvestems. Some claiming it to be beneficial, others useless.
In one of the other Volvo forums there was someone who had installed seals on the outlet valves but found after 100k miles that they had lost their function. The heat of the exhaust valves had made the rubber hard and they had even come loose.

This confusion is the reason why I am so adamant that you check with the engine manufacturer first. Unless it's some well known and well documented design flaw that time unveiled and fixed - go with their design.