This is the how complex insert mode mappings that involve the popup menu are usually written:
iemap <expr> <key> pumvisible() ? "\<another-key>" : "\<key>"
The ternary operator is used to "press"
<another-key> if we are in a popup menu or
<key> if we are not.
Assuming the snippet in your question works (I don't use those plugins), the following mapping should expand the selected snippet if you are in a popup menu or just "press" a regular
imap <expr> <silent> <cr> pumvisible() ?
\ neocomplete#mappings#close_popup() . "<Plug>(neosnippet_jump_or_expand)" :
Note that the code above doesn't check if it is in a neobundle + neosnippet popup menu so I'd suggest putting all that in a function so that you have some elbow room for all your checks (and get a chance to use an actual
if-elseif-else-endif conditional instead of a deep ternary operator.