As a Narn player and Drakh player, I have played both fleets against each other, and the Dilgar.
5 point raid - Narn V Dilgar. Dilgar win, but with only one healthy and 2 crippled ships left
Drakh V Dilgar - Dilgar win, Again all 3 remaining Dilgar ships in bad bad position (of course this is only relevant in a campaign
Drakh V Narn - Drakh win, lost only 1 ship.
6 point Raid in campaign
Narn V Dilgar, Narn win, loose 2 skirmish ships and a crippled battleship, 1 Dilgar battleship flees table, all others destroyed.
As a Narn player, one thing that is your friend is your bigger ships beams, you need range against the dilgar as theirs is poor, if you can knock a couple of ships out at range, you should be OK, Dilgar are pretty tough, concentrate on only one or two ships at a time, the Narn Bat Squad is excelent for this. don't let him get close up and personal, his guns are nastier than yours. Also remember to check if any of his ships have mass drivers before an all stop! Use your Frazis to swarm in his weaker arcs, or taint him by filling an arc full of G'Quan, and watch him panic

My Frazi's dominated the field last time out, as he didn't launch a single Thorum, fool, he thought I had e-mines, but it was a mag cruiser ;-)
Against Drakh, it's difficult to say, the drakh fleet can be difficult to judge and of course you need different tactics against raiders than you do against cruisers, but remember, he has naff hulls, and no fighters. Stay out of the front arc of light raiders, and the rear arc of the cruiser, and your Frazi's or even Goriths should be ok, and rip through him like um, well like a frazi through a drakh ship. You will want the best hull ships ideally, as he has SAP beamyness everywhere. the Rothan should be a solid choice, touch, and it's weapons should punch through the hull and geg effectively, even the Rongoth could be useful, those 20 forward dice against hull 4s and 5's ;-) also remember, the range on the raider weapons, is the same as the range on your secondaries on most ships, you should have all round fire protection
Happy gaming.