alrighty
-so enslaved and heavenly sword were ninja theory's creations correct? so the characters in both of these games are already representing ninja theory, because they are the original works of what ninja theory created, therefore there's no need to put a tribute on the character when the whole character itself is your own original creation. maybe an example will help show what im trying to say. ex. it would be like if capcom was doing their version of a game series, lets use no more heroes as an example. capcom makes a few adjustments to the main protagonist travis touchdown, and on his t-shirt they put a little 8 bit megaman. capcom would have done this as a a tribute to their company, but also because it matches the character's style. however, just because they put this 8 bit megaman on their version of a different company's character, doesn't mean capcom has to put megaman on all of THEIR characters now.
-well a tribute wouldn't fit the style of heavenly sword or enslaved, because well in enslaved you get the feel of a more warrior, rural period of time so i don't think it would've fit into their characters appearance, and with enslaved i guess it could've fit into one of the characters' appearance, but as i said earlier i guess they didn't find that necessary.
-this tribute (the union jack) fits dante's appearance, because a union jack is a trendy fashion symbol. it fits the fashion sense of a punk-rocky type of guy i suppose. and since dante appears to be a punk-rocky type of guy in DmC, it makes perfect sense to me that the flag matches his style.
i hope this has helped.