Mail output with Bash Script

This isn't properly an attempt to answer your question, but I think you should be aware of some fundamental problems with your code.

INVALID=' cat /xxx/xxx/xxxxx | grep 'WORD' | sed 's/$/.\n/g' | grep "$DATE"'

This assigns a simple string to the variable INVALID. Because of quoting issues, s/$/.\n/g is not quoted at all, and will probably be mangled by the shell. (You cannot nest single quotes -- the first single-quoted string extends from the first quote to the next one, and then WORD is outside of any quotes, followed by the next single-quoted string, etc.)

If your intent is to execute this as a command at this point, you are looking for a command substitution; with the multiple layers of uselessness peeled off, perhaps something like

INVALID=$(sed -n -e '/WORD/!d' -e "/$DATE/s/$/./p" /xxx/xxx/xxxx)

which looks for a line matching WORD and $DATE and prints the match with a dot appended at the end -- I believe that's what your code boils down to, but without further insights into what this code is supposed to do, it's impossible to tell if this is what you actually need.

COUNT=$(echo "$INVALID" | wc -c)

This assigns a number to $COUNT. With your static definition of INVALID, the number will always be 62; but I guess that's not actually what you want here.

for x in $HOSTS    
do
  ssh BLA@"$x" $COUNT

This attempts to execute that number as a command on a number of remote hosts (except the loop is over HOSTS and the variable containing the hosts is named just HOST). This cannot possibly be useful, unless you have a battery of commands named as natural numbers which do something useful on these remote hosts; but I think it's safe to assume that that is not what is supposed to be going on here (and if it was, it would absolutely be necessary to explain this in your question).

  if [ "$COUNT" -gt 1 ];
  then

    EMAILTEXT=""
        if [ "$COUNT" -gt 1 ];
        then
                EMAILTEXT="$INVALID"
        fi
  fi

So EMAILTEXT is either an empty string or the value of INVALID. You assigned it to be a static string above, which is probably the source of your immediate question. But even if it was somehow assigned to a command on the local host, why do you need to visit remote hosts and execute something there? Or is your intent actually to execute the command on each remote host and obtain the output?

done | echo -e "$EMAILTEXT" | mail XXXXXXXXXXX.com

Piping into echo makes no sense at all, because it does not read its standard input. You should probably just have a newline after done; though a possibly more useful arrangement would be to have your loop produce output which we then pipe to mail.

Purely speculatively, perhaps something like the following is what you actually want.

for host in $HOSTS; do
    ssh BLA@"$host" sed -n -e '/WORD/!d' -e "/$DATE/s/$/./p" /xxx/xxx/xxxx |
    grep . || echo INVALID
done | mail XXXXXXXXXXX.com

If you want to check that there is strictly more than one line of output (which is what the -gt 1 suggests) then this may need to be a little bit more complicated.

Your command substitution is not working. You should read up on how it works but here are the problem lines:

COUNT=$(echo "$INVALID" | wc -c)
[...]
ssh BLA@"$x" $COUNT

should be:

COUNT_CMD="'${INVALID} | wc -c'"
[...]
COUNT=$(ssh BLA@"$x" $COUNT_CMD)

This inserts the value of $INVALID into the string, and puts the whole thing in single quotes. The single quotes are necessary for the ssh call so the pipes aren't evaluated in the script but on the remote host. (COUNT is changed to COUNT_CMD for readability/clarity.)

EDIT:

I misread the question and have corrected my answer.