No, I get that. But the chart says it's for force carbonation. I took that to mean that if you want to expedite the carbonation process rather than just waiting for the priming sugars to work then you hook up the CO2 at those levels for that type of beer. But you never force carbonate with beer gas because it's too low in CO2 to be effective.
I'm talking about the kegs in my keezer for drinking rather than the ones I'm racking.
That chart shows the resulting carbonation level at a certain pressure and temperature after equilibrium, and since the beer will always reach equilibrium with the applied pressure, this is used both for carbonating and serving your beer. If you carbonate to 2.5 vol, but then serve the beer at a pressure that equates to only 2.0 vol on that chart, the carbonation level will reduce slightly with every pour until it reaches 2.0 vol. If you carb to 2.0 vol, but then serve it at a pressure that equates to 3.0 vol, the carbonation level will continue to increase until it reaches 3.0 vol. This is true regardless of whether you carbonate with priming sugar or force carbonate. What you need to do is figure out your desired carb level and temp, and then use that chart to find the correct carb/serving pressure to achieve that. You then need to make your beer lines long enough to balance this pressure so that you're not pouring a firehose of foam.
Beer gas is a little more complicated. To get that creamy mouthfeel and cascading head from a stout faucet, the beer has to be forced through a restictor plate with small holes in it that causes the CO2 to break apart into super fine bubbles. A large amount of pressure is required to do this, but if 100% CO2 was used the high pressure would result in severely overcarbonated beer. Nitrogen is mixed with the CO2 since it's inert and doesn't dissolve in the beer. This way the pressure can be cranked way up, but the amount of carbonation will remain in check. I'm not sure where you got the idea that beer gas can't be used to force carbonate beer, but it's completely false. You simply have to do it at the much higher pressure that the beer will be served at, usually 30-40 psi for most pre-blended beer gas mixes.
To answer one of your original questions, you can use beer gas to serve any beer. It's most commonly used for stouts and english ales with lower carb levels, but you can use it for anything you want. I've seen all sorts of beers served on nitro at microbreweries, even IPA's. If you think the lower carb level and creamy mouthfeel would go well with a particular beer, stick it on your nitro tap and see if you're right. Worst case scenario is that you don't like it, and switch the keg back to pure CO2 (after venting the super high pressure of course).
If you want a good long read about balancing draught systems with more info than you probably want, have a look here-
https://files.pbworks.com/download/Kb1R2vtz2e/draftquality/47312934/DQM%20Full%20Final%20V2.pdf
I will say that in my experience the actual resistance of beer lines is significantly less than the figures presented in the above link (and elsewhere on the web). I think the 1 foot of line per psi of serving pressure that Goldiggie mentioned above is a pretty good starting point. The only side effect of lines that are too long is slightly slower pours, and since it's much easier to trim a foot off of a line than it is to grow the line a foot longer, it's a good idea to start out longer than you think you'll need. Another benefit to extra long lines is that you'll still get a good pour even if you decide to serve a beer at a higher carb level than you normally use. The restrictor plate in your stout faucet will provide most of the needed resistance for your nitro mix, so a longer line shouldn't be needed there.
