if you are going to use it hard it won't hurt to run at 30 or 25:1
While you are right about the plug fouling part, what you are suggesting about the fuel : oil ratio, in theory, isn't correct.
The problem is that running an excess amount of oil premixed in your fuel can actually make the engine run lean – the total opposite to what most people think. It’s a common misconception that more oil will make the jetting richer.
The oil lubricates the engine, but doesn’t fully burn in the combustion cycle so adding more oil does not make the air : fuel ratio (or jetting) richer in fact it does the opposite – it ‘takes up space’ in the fuel part of the air : fuel ratio thus reducing the amount of fuel in this ratio and leaning out the jetting. This is due to the fact the there is only a certain volume of liquid that can flow through the orifice of a jet and if there is a higher proportion of oil then there is a lower proportion of fuel per unit volume. What’s more the fact that you are also making the liquid more viscous, by adding more oil, further exacerbates the problem as even less liquid will flow through the jet while all the time the volume of air drawn through the carb is staying the same.
However, as you say, in practice it probably won’t hurt it - due to the fact it’s a low technology 8hp engine and the manufacturers tech to jet on the safe side anyway…