I recently found a book in the library with some more evidence about this song.

1965 [copyright 1962]        Elder, Jacob D. _Song Games from Trinidad and Tobago._ The American Folklore Society.

Incidentally, the author seems to have been with Alan Lomax in 1962 when they recorded "Coming Down with a Bunch of Roses" at the San Juan Girls Government School. However, it is implied that his experience with the song goes beyond that one occasion. They example he gives is actually from Tobago in 1928, although it's not clear to me if he collected it all the way back then.

Pg63-64 -- includes score. Lyrics:

1. Lift up you' clotheses,
Comin' dung;
Right up to you' noses,
Comin' dung.

CHO:
Comin' dung with you' bunch o'roses,
Comin' dung;
Comin' dung with you' bunch o'roses,
Comin' dung.

2. Gal show me you' motion,
Gal show me you' motion,

3. Bring in you' lover,
Bring in you' lover,

Notes say that the game is played with 12-24 boys and girls in two files, facing one another. The last pair forms arch with arms, others dance under/through.

"This song was collected from Harrington Benjamin (10) and others at Charlotteville, Tobago in 1928. It is a popular game among children in Tobago although adults usually play it at wakes. This game-song is analagous [sic] to the shanty "Blood Red Roses" as well as to "Bonny Bunch o' Roses." The game which it accompanies is a courtship-game in which the player with the dramatic role—usually female—makes a display of her finery, good looks and dancing styles, and then chooses a lover with whom she dances."

There are a few other notes about this songs scattered in the book.

Pg13 "Brown girl in da ring," "Coming down with you' buncha roses," and "Mizay Marie," played as a rule by adults at a dead-wake from which children are barred, can also be heard among children playing on the neighbourhood compounds on moonlight nights."

Pg 14-15
"Many games, like "Brown gal in da ring" and "Comin' dung with you' buncha roses," have connotations for adults which are far beyond the understanding of the children who learn them from their parents…In "Comin' dung with you' buncha roses," the players must choose partners and arrange themselves in couples to start the game."

Pg50, as references for the song, Elder cites Doerflinger, Adams, Harlow, Hugill. Also says, "Related to the Scottish game "Bonny bunch o' roses"," citing MacLagan.

A couple other game-songs in the collection have "roses" lyrics:

Pg 77, "In my right hand / I have a rose"..."Come in, come in / My charmin' rose." This game actually involves a girl who holds a roses and is admitted into a circle.

Pg105 – "See Miss Lilian So Fresh'n Gay" has lyrics, "See Miss Lilian so fresh 'n gay / With a bunch of roses in her hair". Also involves a girl holding flowers.

Unless one thinks the chanty turned into a game-song, after which it was reinterpreted, these examples suggest pretty strongly that it was a decorated female that was being addressed to "come down" (e.g. down the line).

Possibly cf. "Ring a Ring o' Roses."