Using your National login when booking on Enterprise (or just starting your Enterprise booking through National's website) will preload your contact info, DL, and credit cards you have on file alongside your National number. Credit for the rental will also go towards your National free days, though they take 48ish hours to post versus the almost immediate credit once a National rental is complete. IMO National credits are way better than Enterprise Plus and if you rent frequently from Enterprise then you'll hit Executive Elite at National rather quick and earn a free day every 5th rental.

Outside of that, no there is no upgrade or acknowledgement of status or anything. To the best of my knowledge it doesn't show them your National status, only that you're using your National number versus the Enterprise Plus system. I've had a newer branch rep asked me about National's program; they were newer but didn't know about the aisle, benefit, tiers, etc. They will go through their whole pitch for an upgrade plus the collision/liability waivers, prepaid fuel, etc etc just like they do for every customer. They will ask to see your DL and the credit card every time. If you rent frequently enough from the same branch, being cordial and friendly with the branch staff and manager will net you better chances of nice upgrades and little/no sales pitch than being that person reminding them of their status. I frequent two local Enterprise branches (depending on availability) and I'm recognized as a regular at both. I've had nothing but great experiences thus far but that has nothing to do with being EE, just from chatting with them during drive backs, not complaining about the deposit, and returning the cars in one piece.