I haven't responded on this thread previously but followed it as I started a thread about 2nd showers not that long ago, and it's interesting to see how much this one has now turned to the "dad's role" and whether that role is in any way impacted by his (in/ex)clusion in the shower.
I've attended only 3 baby showers where the father was even present. Two were actually for the same person--and the first was more or less this same (OP's situation). My best (male) friend from law school married a woman with a 10 year old son. I assume she had a baby shower for that baby ten years ago but I couldn't be sure. Either way, her family threw another shower for their first baby together (a girl) and he was present (as was his family but they did not host). Two years later, they had a second shower (also thrown by the mom's sister) for their son. Honestly, I thought at least the second shower was out of line with proper etiquette (not because men were included but because it was their second kid) but figured since it was a different gender, that's why they did it. Either way, if he wasn't one of my best friends in the whole wide world, I would have declined. Instead, I got to go to a party with a ton of great food, cake, and I delivered a gift I would have given them anyway.
The other baby shower with a male present was again, one where I was friends with the dad rather than the mom. (Friend from church growing up.) He and a few male relatives (grandpas and I think one uncle only) hid out the entire time in another part of the house and only came down for the gifts, skipping the games and girlie socialization. My friend was told he was to help open gifts and it was pretty amusing watching him try to figure out what a lot of the items were for (which tells me he may not have been paying attention when they registered). Watching him blush when getting breastfeeding items? Priceless.
For my shower (with DD#1) no men were included and my DH had NO desire to be there. At the time, he was a school teacher and new at a school, and nothing was done for him to welcome him to fatherhood, but many parents of his students & many colleagues gave him gifts on an individual basis.
This time around (as I updated in the other thread) I refused a shower (repeatedly) and got roped into a very fun Girls' Night Out instead. The hostesses took me out to a restaurant we all enjoy and I was consulted only on the guestlist and I kept it very small (7 of us total) and all are mom friends of mine (except my BFF), and none (except BFF) were at my shower for DD#1. The flip to that ironically is that this time DH has had a shower at his school for this child thrown by his colleagues--but that's mostly because there's something in the water there and besides DD#2 due in April there are two other teachers (female) having their 1st and 3rd babies, respectively, so they threw a group shower (sounds naughty!) and included each of them in the celebration. On top of that, the parents of his class this year want to throw a small shower for him also. I think a lot of that is that there are several 'repeat' parents (who had older kids in his class in years past and have a younger child in the class now) and they are looking for any excuse to celebrate him because he is pretty darn awesome.
If you asked him, he would NOT want to go to a shower (didn't come to mine and only came to the 2nd one of the "co-ed" showers I discussed above because he knew there would be carne asada and beer!) but would not want to offend either his colleagues or his students' parents by refusing their offers. (It's a small private school and a huge part of his job is making the parents happy.)