This has been cover many times, on different forums, for many years. The short answer is, no, you can not add surge protection in-line with the boltek antenna.
Actually I found a commercial grade supressor that works fine on it. It's made by Polyphaser and is one of their NX series units.
Talked to Boltek about it and the agreed with the specs it would work fine, and it has for 3 years now.
As long as the surge doesn't exceed (depending on what model you got): "Surge current rating of this device is 300A, 10/1000us per Bellcore 1089 and 3kA, 8x20us per IEC 61000-4-5".
Which would be OK for surges induced by a NEARBY lightning strike. But not for a direct hit.
At 300amps, the conductors of cat5 generally melts down from the strike. In working with Motorola Canopy gear and Othrogon stuff thru the years, sites I have seen hit with these suppressors will have a section of cat5 several feet long totally missing from a direct strike, and usually the suppressor is damaged, but the gear inside the building 9 out of 10 times is still fine. I've got photos of the damage these units have protected against somewhere, that's the reason I started using them, they actually work. Another key is to put decoupling loops in the cat5 before it enters the building, lightning does not like going back uphill.
If I am really wanting to protect the CAT5, I use a Transtector model rated considerably higher and I use double shielded cat5 with the cat5 grounded every 100ft to the tower (better than R56 grounding specs), but those are on very tall structures where it's not a matter of "if" it'll get hit, but how often a year, like where I have my 70ft tall tower cam, and I need it to last, no matter. That tower's been pegged three times since I put up the camera and it's still humming along.
No matter what suppressor you use, a single point of grounding and a well balanced under 5 ohm ground is key to survivability. In my experience, ground potential rise and EMP is what causes the LION share of damage, not direct strikes. (and i'm a 20 year broadcast engineer)