Just because two pairs have high correlation, for e.g. EURUSD and GBPUSD, does not mean that an individual strategy or portfolio expert (even if trading the same one on both pairs) will have high correlation. Inversely, if two individual strategies or portfolio experts have high correlation it does not mean the underlying pairs they trade on have high correlation.
Examples taken from my own trading history over last 4 or so months (100 strategies).
The correlation between the strategies that trade on EURUSD to those that trade on GBPUSD is -0.11 despite EURUSD and GBPUSD having a high correlation. This is because the strategies that are traded on both are different, with different rules, stops, entries etc.
If we look at the positive correlation of those strategies, 104*** = EURUSD, 105*** = GBPUSD, we actually see that there is a bulk of correlation that occurs within EURUSD itself, not beween EURUSD and GBPUSD. I used positive correlation only for the colours because it was easier to format in Excel with conditional formatting. Negative correlation shows a similar result.
This is a birds eye view of 300 strategies. It's hard to see but there is a white line that goes from the top left of the chart to the bottom right. The closer the groups of red are to this white line means that those strategies that trade on the same symbol are more correlated to each other as my magics grouped together and sorted ascending.
Don't take the above as gospel as these are my own results. Grouped into different blocks, added at different times etc.
It's due to these reasons that I believe correlation should be checked and accounted for on the individual strategy level, not the portfolio expert, or symbol level.
To answer your question, yes, you will have more diversification, but you need to be sure that the individual strategies are not correlated.
That being said, you need to be aware of your exposure across symbols.