For the terms of ship-ship combat, crew is a unit. If you lose combat, you lose your ship (at best). Ships have upgrade, their crew does not. If he wants a land unit with "Marine" allowing for use as a Sailor i might allow it, but if he takes them off the ship, he'll need to purchase a new sailor crew or else the ship sits unusable.
Using a real regiment in combat would confer a +1 to combat in melee ship combat simply from having a real strength value to begin with. It wouldn't add to ship combat however as they'd be crewing the ship.
EDIT: Actually i like that
New starting option for you Elf:
1 personal Guard regiment of Marines + Light Warship (You can maintain your 'cannons'. Ret-conning them as not being large enough to confer any sort of Ship combat bonus) - half your upkeep has been paid already (due to you starting with technically twice the units as other people)
New Upgrade added to wiki:
Marine: Counts as a Sailor specialist on a ship. If unit is removed from ship, ship is unusable till sailor is replaced. Confers the unit's str value to crew combat, but no bonus to Ship combat
Upgrade Cost: 1 Ducat
Upkeep: +0.5 Ducats
I haven't gone back and read, CG, but I seem to recall Nuke liking Elfeater's idea and his starting stuff. I don't think he said anything about a heavy regiment, though. I can't help but remember agreement about his crew being useable as soldiers, too.
But what he wants is seriously 3-4x what any other player started with (Aside from the Queen, GMs and sponsored events)