Basically, it's up to you how you play it. Dobro and National mandolins did not come with "square" necks and high nuts, like the "square neck" Hawaiian models of both Dobro and National, meant to be played with a steel bar.
If one wanted to play a resonator mandolin "Hawaiian style," like a bluegrass Dobro, one would want to get the nut and bridge raised so that the strings were well above the frets. This would prevent the player from fretting the strings in the normal manner. Then presumably the mandolin would be tuned to an open chord, and played flat on the lap. Whether the smaller bodied, higher pitched mandolin would sound good played in this way, would be a matter of opinion.
On the other hand, if one wanted to play a resonator mandolin the the manner of "bottleneck" or "slide" guitar, one could use a standard nut and bridge, albeit adjusted to raise the action higher than normal, and "fret" the strings with a tubular slide around one of the fingers of the fretting hand. I assume that's what the performers who play "slide" mandolin are doing. Many "slide" guitar players tune to an open chord, but others work out of standard tuning, and the "slide" mandolin player could choose one approach or the other.
Resonator instruments are noted for having longer "sustain," which makes them good choices for "slide" playing. However, "slide" mandolin is a very unusual method; Sam Bush does it, but most of the blues mandolin players I've heard fret the strings in the normal manner, without using a slide.
If you're interested in experimenting with resonator mandolin and not spending a ton of money, Johnson makes a Pac-rim chrome or nickel plated brass resonator mandolin for a reasonable price. Not a miracle of craftsmanship, but a decent introduction to the small world of the resonator mandolin.
Allen Hopkins
Gibsn: '54 F5 3pt F2 A-N Custm K1 m'cello
Natl Triolian Dobro mando
Victoria b-back Merrill alumnm b-back
H-O mandolinetto
Stradolin Vega banjolin
Sobell'dola Washburn b-back'dola
Eastmn: 615'dola 805 m'cello
Flatiron 3K OM
Bookmarks